CCBC-263 Skip unfinished SASL commands

During rebalance, it is possible that the newly added server doesn't
have chance to finish SASL auth before the cluster will push config
update, in this case packet relocator messing cookies.

Also the patch makes sure that SASL command/cookie isn't mixing with
other commands

Change-Id: Ic3fb01b4a39d2e8e68c690c264a2918d631d9602