Use GLANCE_PASS as keystone password

According to
https://wiki.openstack.org/wiki/Documentation/Conventions#Install_Guide
it should be GLANCE_PASS for keystone, and GLANCE_DBPASS for mysql. The
guide uses GLANCE_DBPASS for both - fix this.

Cherry-Pick: https://review.openstack.org/#/c/53002/
Change-Id: I2db43d383db52bfe50bd988a3b30b848b2d7b1ce
backport: havana
Closes-Bug: #1242860
Merge "Use GLANCE_PASS as keystone password" into stable/havana