Refresh only one plugin after install/upgrade
Refresh only one plugin after install/upgrade

When installing or upgrading a single plugin, there is no need to
refresh the entire list. 

Change-Id: Ib2d7026b786e6f8628c7294f93596025228d8365

GerritCodeReview/plugins_plugin-manager,GerritCodeReview/plugins_plugin-manager,GerritCodeReview/plugins_plugin-manager