BREAK: remove auto-init behaviour

In the event that the project could not be found, stop BuildStream from
asking if the user would like to create a new project. Exit with error
instead, and give a hint to the user in case they're new.

As proposed on the mailing list here:
https://mail.gnome.org/archives/buildstream-list/2018-December/msg00082.html

The new interaction looks like this:

    $ bst show nonsuch.bst
    No project found. You can create a new project like so:

        bst init

    Error loading project: None of ['project.conf', '.bstproject.yaml']
    found in '/src/temp/blah' or any of its parent directories

Fixes #826

4 files changed, 16 insertions, 24 deletions

diff --git a/NEWS b/NEWS
index 7e6ec8477..7ee63f952 100644
--- a/NEWS
+++ b/NEWS
@@ -30,6 +30,12 @@ buildstream 1.3.1
     make changes to their .bst files if they are expecting these environment
     variables to be set.
 
+  o BREAKING CHANGE: The 'auto-init' functionality has been removed. This would
+    offer to create a project in the event that bst was run against a directory
+    without a project, to be friendly to new users. It has been replaced with
+    an error message and a hint instead, to avoid bothering folks that just
+    made a mistake.
+
   o Failed builds are included in the cache as well.
     `bst checkout` will provide anything in `%{install-root}`.
     A build including cached fails will cause any dependant elements
@@ -67,8 +73,8 @@ buildstream 1.3.1
     instead of just a specially-formatted build-root with a `root` and `scratch`
     subdirectory.
 
-  o The buildstream.conf file learned new 'prompt.auto-init',
-    'prompt.really-workspace-close-remove-dir', and
+  o The buildstream.conf file learned new
+    'prompt.really-workspace-close-remove-dir' and
     'prompt.really-workspace-reset-hard' options. These allow users to suppress
     certain confirmation prompts, e.g. double-checking that the user meant to
     run the command as typed.
diff --git a/buildstream/_context.py b/buildstream/_context.py
index a3487a794..e0eea99ff 100644
--- a/buildstream/_context.py
+++ b/buildstream/_context.py
@@ -117,10 +117,6 @@ class Context():
         # Whether or not to attempt to pull build trees globally
         self.pull_buildtrees = None
 
-        # Boolean, whether to offer to create a project for the user, if we are
-        # invoked outside of a directory where we can resolve the project.
-        self.prompt_auto_init = None
-
         # Boolean, whether we double-check with the user that they meant to
         # remove a workspace directory.
         self.prompt_workspace_close_remove_dir = None
@@ -258,12 +254,10 @@ class Context():
         prompt = _yaml.node_get(
             defaults, Mapping, 'prompt')
         _yaml.node_validate(prompt, [
-            'auto-init', 'really-workspace-close-remove-dir',
+            'really-workspace-close-remove-dir',
             'really-workspace-close-project-inaccessible',
             'really-workspace-reset-hard',
         ])
-        self.prompt_auto_init = _node_get_option_str(
-            prompt, 'auto-init', ['ask', 'no']) == 'ask'
         self.prompt_workspace_close_remove_dir = _node_get_option_str(
             prompt, 'really-workspace-close-remove-dir', ['ask', 'yes']) == 'ask'
         self.prompt_workspace_close_project_inaccessible = _node_get_option_str(
diff --git a/buildstream/_frontend/app.py b/buildstream/_frontend/app.py
index 87b85cd37..96e3c60ae 100644
--- a/buildstream/_frontend/app.py
+++ b/buildstream/_frontend/app.py
@@ -219,13 +219,13 @@ class App():
                                    default_mirror=self._main_options.get('default_mirror'))
         except LoadError as e:
 
-            # Let's automatically start a `bst init` session in this case
-            if e.reason == LoadErrorReason.MISSING_PROJECT_CONF and self.interactive:
-                click.echo("A project was not detected in the directory: {}".format(directory), err=True)
-                if self.context.prompt_auto_init:
-                    click.echo("", err=True)
-                    if click.confirm("Would you like to create a new project here?"):
-                        self.init_project(None)
+            # Help users that are new to BuildStream by suggesting 'init'.
+            # We don't want to slow down users that just made a mistake, so
+            # don't stop them with an offer to create a project for them.
+            if e.reason == LoadErrorReason.MISSING_PROJECT_CONF:
+                click.echo("No project found. You can create a new project like so:", err=True)
+                click.echo("", err=True)
+                click.echo("    bst init", err=True)
 
             self._error_exit(e, "Error loading project")
 
diff --git a/buildstream/data/userconfig.yaml b/buildstream/data/userconfig.yaml
index 4429d1f6d..6351619aa 100644
--- a/buildstream/data/userconfig.yaml
+++ b/buildstream/data/userconfig.yaml
@@ -112,14 +112,6 @@ logging:
 #
 prompt:
 
-  # Whether to create a project with 'bst init' if we are invoked outside of a
-  # directory where we can resolve the project.
-  #
-  #  ask - Prompt the user to choose.
-  #  no  - Never create the project.
-  #
-  auto-init: ask
-
   # Whether to really proceed with 'bst workspace close --remove-dir' removing
   # a workspace directory, potentially losing changes.
   #