Cleanup in SiteLinkTableTest

add protected variable to use across tests in the class

Change-Id: Ic62d508374f6bd5f2f4f0fe25805588a5a5e97a1
Add method to get EntityId for a SiteLink

Change-Id: I9be83d2a259bae686f946f3879430903aab8b8a6
Merge changes I9be83d2a,Ic62d5083

* changes:
  Add method to get EntityId for a SiteLink
  Cleanup in SiteLinkTableTest