Expect python3 client package in CentOS8

In CentOS, we expect to have python3 client package in 8.x while we
expect to have python2 in 7.x .
Fix unit tests to expect the correct version according to os major
version.

Change-Id: Ifdc8e09197f15720d585598b54ba9427f436dc3a

spec/classes/aodh_client_spec.rb

@@ -31,7 +31,11 @@ describe 'aodh::client' do
         when 'Debian'
           { :client_package_name => 'python3-aodhclient' }
         when 'RedHat'
-          { :client_package_name => 'python-aodhclient' }
+          if facts[:operatingsystemmajrelease] > '7'
+            { :client_package_name => 'python3-aodhclient' }
+          else
+            { :client_package_name => 'python-aodhclient' }
+          end
         end
       end