Bug 1092428: Support 'pgo_only_suites' r=bhearsum

If a suite is listed in this branch-level configuration, then it will only be
run on PGO builds. Regular opt builds won't trigger these talos suites.
bug 1102283: figure out firefox 34 release mechanics - shorten more stuff. r=rail
Merging from default

changeset:   3964:60e31b9c1457
parent:      3961:7488410fce9b
user:        Chris AtLee <catlee@mozilla.com>
date:        Thu Nov 20 16:21:46 2014 -0500
summary:     Bug 1092428: Support 'pgo_only_suites' r=bhearsum

changeset:   3966:1674ff687951
parent:      3964:60e31b9c1457
user:        Ben Hearsum <bhearsum@mozilla.com>
date:        Fri Nov 21 13:36:49 2014 -0500
summary:     bug 1102283: figure out firefox 34 release mechanics - shorten more stuff. r=rail

--HG--
branch : production-0.8