config: Implemented multi-target support

With this patch support for building multiple targets in parallel with
bitbake is now supported.

Changes:

  - Its now possible to state a list of targets under the target key in
    the configuration file.

    Example:

        target:
          - product-image
          - product-update-image

  - Its now possible to define multiple targets in the kas command line.

    Example:

        $ kas build --target product-image --target product-update-image \
          kas.yml

  - Its now possible to define multiple targets via the environment:

    Example:

        $ export KAS_TARGET="product-image product-update-image"
        $ kas build kas.yml

Signed-off-by: Claudius Heine <ch@denx.de>

kas/__version__.py

@@ -26,5 +26,5 @@ __license__ = 'MIT'
 __copyright__ = 'Copyright (c) Siemens AG, 2017'
 
 __version__ = '0.13.0'
-__file_version__ = 3
+__file_version__ = 4
 __compatible_file_version__ = 1

kas/build.py

@@ -55,6 +55,7 @@ class Build:
         bld_psr.add_argument('config',
                              help='Config file')
         bld_psr.add_argument('--target',
+                             action='append',
                              help='Select target to build')
         bld_psr.add_argument('--task',
                              help='Select which task should be executed')
@@ -118,6 +119,6 @@ class BuildCommand(Command):
         """
         # Start bitbake build of image
         bitbake = find_program(config.environ['PATH'], 'bitbake')
-        run_cmd([bitbake, '-k', config.get_bitbake_target(),
-                 '-c', config.get_bitbake_task()],
+        run_cmd([bitbake, '-k', '-c', config.get_bitbake_task()] +
+                config.get_bitbake_targets(),
                 env=config.environ, cwd=config.build_dir)

kas/config.py

@@ -209,13 +209,19 @@ class Config:
             repo_dict[repo] = rep
         return repo_dict
 
-    def get_bitbake_target(self):
+    def get_bitbake_targets(self):
         """
-            Return the bitbake target
+            Returns a list of bitbake targets
         """
-        return os.environ.get('KAS_TARGET',
-                              self._config.get('target',
-                                               'core-image-minimal'))
+        environ_targets = [i
+                           for i in os.environ.get('KAS_TARGET', '').split()
+                           if i]
+        if environ_targets:
+            return environ_targets
+        target = self._config.get('target', 'core-image-minimal')
+        if isinstance(target, str):
+            return [target]
+        return target
 
     def get_bitbake_task(self):
         """

kas/shell.py

@@ -52,6 +52,7 @@ class Shell:
         sh_prs.add_argument('config',
                             help='Config file')
         sh_prs.add_argument('--target',
+                            action='append',
                             help='Select target to build',
                             default='core-image-minimal')
         sh_prs.add_argument('--skip',