Adds RHEL common element

This element contains the installation steps common to RHEL
operating system versions.

Change-Id: I37cce0bd5b5d31525f1335ecd416be570d36ad61

elements/rhel-common/README.md

@@ -0,0 +1 @@
+This element contains the common installation steps between RHEL os releases.

elements/rhel-common/pre-install.d/00-rhsm

@@ -44,7 +44,11 @@ if [ -n "$DIB_RHSM_USER" ] && [ -n "$DIB_RHSM_PASSWORD" ] ; then
             subscription-manager attach --pool $DIB_RHSM_POOL
         fi
         # optional repo required for diskimage-builder dependency
-        repos="--enable rhel-6-server-optional-rpms"
+        if [ "$DISTRO_NAME" == "rhel7" ]; then
+            repos="--enable rhel-7-server-optional-rpms"
+        else
+            repos="--enable rhel-6-server-optional-rpms"
+        fi
         if [[ -n "$DIB_RHSM_REPOS" ]]; then
             for repo in $DIB_RHSM_REPOS; do
                 repos="$repos --enable $repo"

elements/rhel/element-deps

@@ -1,4 +1,5 @@
 cache-url
 dib-run-parts
+rhel-common
 rpm-distro
 yum

elements/rhel7/element-deps

@@ -1,6 +1,7 @@
 cache-url
 dib-run-parts
 redhat-common
+rhel-common
 rpm-distro
 source-repositories
 yum