Moved tests to CirrusSearch repository

See also the commit[1] in CirrusSearch repository that moves the tests
there and the
commit[2] in mediawiki/selenium repository that documents changes in
Jenkins jobs.

1: https://gerrit.wikimedia.org/r/#/c/113131/
2: https://gerrit.wikimedia.org/r/#/c/113138/

Bug: 61311
Change-Id: I5378b1d60fa26a9d15565970464ed1f4f56b7055