Add support for Baserock definitions version 7

This adds a new 'Defaults' class to represent definitions defaults

The Python 'jsonschema' module is used to validate the contents of the
Defaults file. This module is already included in Baserock 'build' and
'devel' reference systems by way of the 'openstack-common' stratum.

This commit embeds a copy of the JSON-Schema schema for the DEFAULTS
file. I think the canonical location of this schema should be in the
reference definitions.git, for now. In future, the schemas should maybe
have their own repos. Either way, Morph should embed a copy for the time
being so that we are sure the schema matches how Morph expects to parse
the file.

Morph's automated tests are all updated to use definitions version 7.
I removed most of the tests for built-in build systems, because the
built-ins themselves are no longer part of Morph. Only the mechanism for
defining them needs to be tested now.

Change-Id: I65f8f1c967683ef605852bfae5c68518e53f9981

1 files changed, 9 insertions, 5 deletions

diff --git a/morphlib/morphologyfinder.py b/morphlib/morphologyfinder.py
index 9184c160..a334350e 100644
--- a/morphlib/morphologyfinder.py
+++ b/morphlib/morphologyfinder.py
@@ -15,9 +15,7 @@
 # =*= License: GPL-2 =*=
 
 
-import cliapp
-
-import morphlib
+import errno
 
 
 class MorphologyFinder(object):
@@ -33,9 +31,15 @@ class MorphologyFinder(object):
         self.gitdir = gitdir
         self.ref = ref
 
-    def read_file(self, filename):
+    def read_file(self, filename, allow_missing=False):
         '''Return the text of a file inside the Git repo.'''
-        return self.gitdir.read_file(filename, self.ref)
+        try:
+            return self.gitdir.read_file(filename, self.ref)
+        except IOError as e:
+            if allow_missing and e.errno == errno.ENOENT:
+                return None
+            else:
+                raise
 
     def list_morphologies(self):
         '''Return the filenames of all morphologies in the (repo, ref).