Add ability to install in HA mode

As long as we decide to use LBaaS in HA (with lack of rescheduling),
such mode added to plugin.

Change-Id: I84ca981f2ad5919bb804fd9349d55eb11476b324
Closes-Bug: #1423481

.gitreview

@@ -0,0 +1,4 @@
+[gerrit]
+host=review.openstack.org
+port=29418
+project=stackforge/fuel-plugin-neutron-lbaas.git

metadata.yaml

@@ -12,12 +12,12 @@ fuel_version: ['6.0']
 releases:
   - os: ubuntu
     version: 2014.2-6.0
-    mode: ['multinode']
+    mode: ['multinode','ha']
     deployment_scripts_path: deployment_scripts/
     repository_path: repositories/ubuntu
   - os: centos
     version: 2014.2-6.0
-    mode: ['multinode']
+    mode: ['multinode','ha']
     deployment_scripts_path: deployment_scripts/
     repository_path: repositories/centos