Allow to specify an empty package list in pkg_map

An empty package list can be provided in a pkg_map file for those
cases were there is no need to install the package.

Change-Id: I0df8c6848ec4ac9e0f90790f14e8eb5399650339

elements/pkg-map/README.md

@@ -23,8 +23,10 @@ Provides the following:
      + suse: includes the opensuse distro
 
    The most specific section takes priority.
+   An empty package list can be provided.
    Example for Nova and Glance (NOTE: using fictitious package names
-   for Fedora to provide a good example!)
+   for Fedora and package mapping for suse family to provide a good
+   example!)
 
    Example format:
     {
@@ -38,6 +40,9 @@ Provides the following:
         "redhat": {
           "nova_package": "openstack-nova",
           "glance_package": "openstack-glance"
+        },
+        "suse": {
+          "nova_package": ""
         }
       },
       "default": {
@@ -60,6 +65,10 @@ Provides the following:
 
    Returns: nova
 
+   pkg-map --element nova-compute --distro opensuse nova_package
+
+   Returns:
+
  * This output can be used to filter what other tools actually install
    (install-packages can be modified to use this for example)
 

elements/pkg-map/bin/pkg-map

@@ -60,7 +60,9 @@ def main():
 
     # Parse mapping data in this form using distro/family/default
     # Most specific takes priority (distro is most specific).
-    # Example for Nova and Glance (using fictitious name for Fedora)
+    # An empty package list can be provided.
+    # Example for Nova and Glance (using fictitious name for Fedora and SUSE
+    # and package mapping for SUSE family)
     # {
     #   "distro": {
     #     "fedora": {
@@ -72,7 +74,10 @@ def main():
     #     "redhat": {
     #       "nova_package": "openstack-nova",
     #       "glance_package": "openstack-glance"
-    #     }
+    #     },
+    #     "suse": {
+    #       "nova_package": ""
+    #    }
     #   },
     #   "default": {
     #     "nova_package": "nova",
@@ -92,6 +97,8 @@ def main():
         pkg_name = name_map.get(name)
         if pkg_name:
             print(pkg_name)
+        elif name in name_map:
+            continue
         else:
             err_msg = 'Missing package name for distro/element: %s/%s'
             print(err_msg % (args.distro, args.element))