Introduce a new "create-instance" command to docker-cubicweb-helper

This will help users not using onbuild images to create an instance easily.

Dockerfile.onbuild

@@ -6,4 +6,4 @@ ONBUILD USER root
 ONBUILD COPY . /src/
 ONBUILD RUN pip install -e /src
 ONBUILD USER cubicweb
-ONBUILD RUN cubicweb-ctl create $(docker-cubicweb-helper get-cube) $CW_INSTANCE --automatic --no-db-create
+ONBUILD RUN docker-cubicweb-helper create-instance

README.rst

@@ -120,7 +120,7 @@ For example, given you're in the source tree of `cubicweb-blog`_::
    COPY . /src
    RUN pip install -e /src
    USER cubicweb
-   RUN cubicweb-ctl create blog $CW_INSTANCE --automatic --no-db-create
+   RUN docker-cubicweb-helper create-instance
 
 
 In case of out-of-source tree or not installing from /src directory, you will
@@ -130,8 +130,8 @@ also have to set the ``CUBE`` environment variable::
    USER root
    RUN pip install cubicweb-blog
    USER cubicweb
-   RUN cubicweb-ctl create blog $CW_INSTANCE --automatic --no-db-create
    ENV CUBE=blog
+   RUN docker-cubicweb-helper create-instance
 
 How to run resulting images ?
 -----------------------------

docker-cubicweb-helper

@@ -28,6 +28,12 @@ def get_cube():
     print(_get_cube())
 
 
+def create_instance():
+    subprocess.check_call([
+        'cubicweb-ctl', 'create', _get_cube(), os.environ['CW_INSTANCE'],
+        '--automatic', '--no-db-create'])
+
+
 if __name__ == '__main__':
     logging.basicConfig(format='%(asctime)-15s %(message)s')
     LOG.setLevel(logging.INFO)
@@ -36,6 +42,9 @@ if __name__ == '__main__':
     get_cube_parser = sub.add_parser(
         'get-cube', help='get top level cubicweb cube')
     get_cube_parser.set_defaults(func=get_cube)
+    create_instance_parser = sub.add_parser(
+        'create-instance', help='create a cubicweb instance')
+    create_instance_parser.set_defaults(func=create_instance)
     args = vars(parser.parse_args())
     func = args.pop('func')
     sys.exit(func(**args))