mutable state checksums part#2: persistence changes

[venkat1109]

This patch contains the cassandra persistence changes to support mutable state checksums. This is a follow up to #2941

[wxing1292]

0.24?

[venkat1109]

This change is backwards compatible with 0.23 and so this is set to 0.23

[wxing1292]

i would put checksum in a seperate group, e.g.

InternalWorkflowMutableState struct {
		ExecutionInfo    *InternalWorkflowExecutionInfo
		ReplicationState *ReplicationState
		VersionHistories *DataBlob

		ActivityInfos       map[int64]*InternalActivityInfo
		TimerInfos          map[string]*TimerInfo
		ChildExecutionInfos map[int64]*InternalChildExecutionInfo
		RequestCancelInfos  map[int64]*RequestCancelInfo
		SignalInfos         map[int64]*SignalInfo
		SignalRequestedIDs  map[string]struct{}
		BufferedEvents      []*DataBlob

		Checksum            checksum.Checksum
}

[venkat1109]

I assume this is simply personal preference. In general, this is something that is not auto enforcable by gofmt etc. And so, over time, your personal preference for grouping this separately is not sustainable. I will group this separately for now. But philosophically, I am not a big fan these type of semi-enforced groupings (unless there is strong reasons like struct packing in C/C++)

[wxing1292]

one more thing, where is the impl for SQL?

[coveralls]

Coverage increased (+0.02%) to 67.982% when pulling 178ad52 on venkat1109:v_ms_crc_db into 95786aa on uber:master.

[venkat1109]

one more thing, where is the impl for SQL?
SQL is currently not supported. I will consider adding support for it after rolling this out. There will be a github task created though for anyone to pick that up.