Add build_system property to config file

This allows to pre-select the build system, specifically avoiding
confusion when kas-container is accidentally not called with --isar for
an isar config. For that, build_system needs to be defined in the
lop-level config file passed to kas-container.

Theoretically, this also allows to combine layers which have both
oe-init-build-env and isar-init-build-env scripts.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kas/configschema.py

@@ -1,6 +1,6 @@
 # kas - setup tool for bitbake based projects
 #
-# Copyright (c) Siemens AG, 2017-2018
+# Copyright (c) Siemens AG, 2017-2020
 #
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the 'Software'), to deal
@@ -72,6 +72,10 @@ CONFIGSCHEMA = {
                 },
             },
         },
+        'build_system': {
+            'type': 'string',
+            'enum': ['openembedded', 'oe', 'isar'],
+        },
         'defaults': {
             'type': 'object',
             'additionalProperties': False,