Add --set argument to prepare command

This new argument will allow special ceph variables to be added to the
template file overcloud_containers.yaml.j2. For example if the
following existed in the template file:
  {% set ceph_namespace=ceph_namespace or "ceph" %}
  {% set ceph_daemon=ceph_daemon or "daemon" %}
  {% set ceph_tag=ceph_tag or "tag-build-master-jewel-centos-7" %}
  - imagename: "{{ ceph_namespace }}/{{ ceph_daemon }}:{{ ceph_tag }}"

Then the --set argument will allow making substitutions on these
values, for example:
  openstack overcloud container image prepare \
      --namespace tripleoupstream \
      --tag latest \
      --images-file overcloud_containers.yaml \
      --set ceph_namespace=myceph \
      --set ceph_tag=latest \
      --env-file $HOME/docker_registry.yaml

Change-Id: Ie12dbab0f4d7f20d14a764abb9095fd8b326c700

tripleoclient/tests/v1/overcloud_image/test_container_image.py

@@ -120,6 +120,12 @@ class TestContainerImagePrepare(TestPluginV1):
             images_file,
             '--env-file',
             env_file,
+            '--set',
+            'ceph_namespace=myceph',
+            '--set',
+            'ceph_image=mydaemon',
+            '--set',
+            'ceph_tag=mytag',
         ]
         self.cmd.app.command_options = arglist
         verifylist = []
@@ -144,7 +150,10 @@ class TestContainerImagePrepare(TestPluginV1):
             name_prefix='os-',
             name_suffix='foo',
             namespace='tripleo',
-            tag='passed-ci'
+            tag='passed-ci',
+            ceph_image='mydaemon',
+            ceph_namespace='myceph',
+            ceph_tag='mytag'
         )
         ci_data = {
             'container_images': [{

tripleoclient/v1/container_image.py

@@ -22,6 +22,7 @@ import sys
 import tempfile
 
 from osc_lib.command import command
+from osc_lib import exceptions as oscexc
 from osc_lib.i18n import _
 import yaml
 
@@ -218,6 +219,13 @@ class PrepareImageFiles(command.Command):
             help=_("Override the default name suffix substitution.\n"
                    "Default is empty."),
         )
+        parser.add_argument(
+            '--set',
+            metavar='<variable=value>',
+            action='append',
+            help=_('Set the value of a variable in the template, even if it '
+                   'has no dedicated argument such as "--suffix".')
+        )
         parser.add_argument(
             "--exclude",
             dest="excludes",
@@ -244,6 +252,18 @@ class PrepareImageFiles(command.Command):
         )
         return parser
 
+    def parse_set_values(self, subs, set_values):
+        if not set_values:
+            return
+        for s in set_values:
+            try:
+                (n, v) = s.split(('='), 1)
+                subs[n] = v
+            except ValueError:
+                msg = _('Malformed --set(%s). '
+                        'Use the variable=value format.') % s
+                raise oscexc.CommandError(msg)
+
     def write_env_file(self, params, env_file):
 
         with os.fdopen(os.open(env_file,
@@ -265,6 +285,7 @@ class PrepareImageFiles(command.Command):
             'name_prefix': parsed_args.prefix,
             'name_suffix': parsed_args.suffix,
         }
+        self.parse_set_values(subs, parsed_args.set)
 
         def ffunc(entry):
             imagename = entry.get('imagename', '')