Minor/useful tweaks to Sahara repo descriptions

plugins->plugin (each repo contains just one plugin)

Improve grammar/diction in Sahara description (borrowed from version
found in governance repo)

Change-Id: I5c291bed0be444688fe4a99e3be83e6a0e444fa2

gerrit/projects.yaml

@@ -4879,9 +4879,8 @@
   use-storyboard: true
   groups:
     - sahara
-  description: Sahara aims to provide users with simple means to provision a Hadoop
-    cluster by specifying several parameters like Hadoop version, cluster topology,
-    nodes hardware details and a few more.
+  description: Sahara provides a scalable data processing stack and associated
+    management interfaces.
   options:
     - translate
 - project: openstack/sahara-dashboard
@@ -4904,7 +4903,7 @@
   description: Disk image elements for Sahara
   acl-config: /home/gerrit2/acls/openstack/sahara-etc.config
 - project: openstack/sahara-plugin-ambari
-  description: Ambari provisioning plugins for Sahara
+  description: Ambari provisioning plugin for Sahara
   use-storyboard: true
   acl-config: /home/gerrit2/acls/openstack/sahara.config
   groups:
@@ -4912,7 +4911,7 @@
   options:
     - translate
 - project: openstack/sahara-plugin-cdh
-  description: CDH provisioning plugins for Sahara
+  description: CDH provisioning plugin for Sahara
   use-storyboard: true
   acl-config: /home/gerrit2/acls/openstack/sahara.config
   groups:
@@ -4920,7 +4919,7 @@
   options:
     - translate
 - project: openstack/sahara-plugin-mapr
-  description: MapR provisioning plugins for Sahara
+  description: MapR provisioning plugin for Sahara
   use-storyboard: true
   acl-config: /home/gerrit2/acls/openstack/sahara.config
   groups:
@@ -4928,7 +4927,7 @@
   options:
     - translate
 - project: openstack/sahara-plugin-spark
-  description: Spark provisioning plugins for Sahara
+  description: Spark provisioning plugin for Sahara
   use-storyboard: true
   acl-config: /home/gerrit2/acls/openstack/sahara.config
   groups:
@@ -4936,7 +4935,7 @@
   options:
     - translate
 - project: openstack/sahara-plugin-storm
-  description: Storm provisioning plugins for Sahara
+  description: Storm provisioning plugin for Sahara
   use-storyboard: true
   acl-config: /home/gerrit2/acls/openstack/sahara.config
   groups:
@@ -4944,7 +4943,7 @@
   options:
     - translate
 - project: openstack/sahara-plugin-vanilla
-  description: Plain Hadoop (vanilla) provisioning plugins for Sahara
+  description: Plain Hadoop (vanilla) provisioning plugin for Sahara
   use-storyboard: true
   acl-config: /home/gerrit2/acls/openstack/sahara.config
   groups: