Tuning of galera gcache size that allows override of individual wsrep_provider_options in tripleo deployment

Issue

• Because of the high instance create/delete rate in RHOSP cluster the default gcache.size of 128 mb leaves with maintenance windows of less than 30 minutes.
• Hardware replacements takes more than one hour and it causes SST with default gcache.size resulting entire load on 3rd controller because the doner and receiver nodes are locked during SST.Sometimes this situation of single node available during SST results in broken cluster with high instance create/delete rate.