Add jobs for wikibase

Will be triggered by Wikimedia Jenkins on an instance managed
by the Wikidata team.

Created jobs:
* mwext-Wikibase-repo-api-tests
* mwext-Wikibase-repo-getentities-api-tests
* mwext-Wikibase-client-tests

Updated job:
* mwext-Wikibase-repo-tests

Change-Id: Ifa58a060c3e792ed9efdac04e3737a129cc72451