Rename tests.ini to tests.ini.sample

This allows modifications to the actual test configuration file without
having git complain about it.

Change-Id: I54a0bfb7f5629a4a3b4d220ffe3d1d37c4342448
Reviewed-on: http://review.couchbase.org/26319
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>