Make gate-rally-install-bare-centos6 non voting

Temporary make gate-rally-install-bare-centos6 non voting.
For some reason this job is failing with "NOT_REGISTERED" flag.

So make it temporary non voting, until things are fixed

Change-Id: Ic9e71ffd17a7949d25a46a3cc6e4e552869b5936
Merge "Make gate-rally-install-bare-centos6 non voting"