Backport frontier_client from CMSSW_7_0_X.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Backport git from CMSSW_7_0_X.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #177 from davidlt/53x-slc6-git-frontier_client

[CMSSW_5_3_X] Backport git and frontier_client from CMSSW_7_0_X