Update Gerrit image version

* update gerrit to 2019.2.6 with v2.15.17 version of Gerrit;
* set IGNORE_VERSIONCHECK var for Gerrit container, for
  full reindex data before start for upgrade [0,1]

[0] https://www.gerritcodereview.com/2.13.html#online-reindexing
[1] https://www.gerritcodereview.com/2.14.html#reindex-for-new-groups-index

Change-Id: I02924e49343ae1f2ecaa1c3409a9bf79df63120e
Related-Prod: PROD-33894
2 files changed