Add RedHat derivatives support for OSA Magnum role

I got a failure when running OSA on Centos with Magnum,
this file adds the package names for RedHat derivatives.

Change-Id: Ia355f15b6c2c9d80447e227660f7037b3dfdc58e

meta/main.yml

@@ -24,6 +24,9 @@ galaxy_info:
   - name: Ubuntu
     versions:
     - xenial
+  - name: EL
+    versions:
+    - 7
   # Below are all categories currently available. Just as with
   # the platforms above, uncomment those that apply to your role.
   galaxy_tags:

vars/redhat.yml

@@ -0,0 +1,26 @@
+---
+# Copyright 2017, Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Common apt packages
+magnum_distro_packages:
+  - python-devel
+  - openssl-devel
+  - libxml2-devel
+  - libxslt-devel
+  - postgresql-devel
+  - git
+  - libffi-devel
+  - gettext
+  - gcc