Add morph cross-bootstrap

Cross-bootstrap is a way to build baserock on an architecture that
does not currently have Baserock. It can be used by `morph
cross-bootstrap <ARCH> <REPO> <REF> <MORPH>`, and will build an artifact
that can be used as a root filesystem with a basic build environment
with a script named `native-bootstrap` which will build and install
every chunk in the system.

If done with a devel system, this will give you a suitable environment
for building a proper Baserock system.

This does not currently provide a kernel for the target architecture.

Apart from adding the cross-bootstrap plugin, it also makes the
following changes:

* Moves the lit of valid_archs into morphlib (instead of locally-scoped
  in MorphologyFactory)
* BuildCommand takes an extra argument, build_env
* split BuildCommand's get_artifact_object into create_source_pool and
  resolve_artifacts (plus changes things that use get_artifact_object to
  use the new way)
* setup_mounts finds out whether to do so by whether build_mode is
 'staging', instead of by whether the setting 'staging-chroot' is true.
* Makes ChunkBuilder's get_sources use the
  morphlib.builder2.extract_sources() method, and moved
  set_mtime_recursively into morphlib.builder2, since it's not currently
  used anywhere else.
* moved ChunkBuilder's get_commands into the Morphology class (plus
  changes to anything that used get_commands)

1 files changed, 35 insertions, 0 deletions

diff --git a/morphlib/morph2_tests.py b/morphlib/morph2_tests.py
index 1a0b4822..9de23e56 100644
--- a/morphlib/morph2_tests.py
+++ b/morphlib/morph2_tests.py
@@ -344,3 +344,38 @@ class MorphologyTests(unittest.TestCase):
         dummy = Morphology(self.stratum_text)
         output_dict = dummy._apply_changes(live_dict, original_dict)
         self.assertEqual(original_dict, output_dict)
+
+    def test_uses_morphology_commands_when_given(self):
+        m = Morphology('''
+            {
+                'name': 'foo',
+                'kind': 'chunk',
+                'build-system': 'dummy',
+                'build-commands': ['build-it']
+            }
+        ''')
+        cmds = m.get_commands('build-commands')
+        self.assertEqual(cmds, ['build-it'])
+
+    def test_uses_build_system_commands_when_morphology_doesnt(self):
+        m = Morphology('''
+            {
+                'name': 'foo',
+                'kind': 'chunk',
+                'build-system': 'dummy',
+            }
+        ''')
+        cmds = m.get_commands('build-commands')
+        self.assertEqual(cmds, ['echo dummy build'])
+
+    def test_uses_morphology_commands_when_morphology_has_empty_list(self):
+        m = Morphology('''
+            {
+                'name': 'foo',
+                'kind': 'chunk',
+                'build-system': 'dummy',
+                'build-commands': []
+            }
+        ''')
+        cmds = m.get_commands('build-commands')
+        self.assertEqual(cmds, [])