Refs #106: remove ist_sst_ and unnecessary gcs_.join
Refs #106: remove if condition. call gcs_.join anyway when sst is done
Refs #106: add join flags to ist sender which means join back to cluster when it exits. it is introduced because sometimes sst_sent may not be called.
Refs #106: call gcs_join right after IST. otherwise node could serve IST or SST for only one node, which is not we expect
Refs #106: remove duplicate condition
Merge pull request #146 from codership/gh106

Gh106
Merge branch '3.x' into gh71