MB-11417: Datatype validation for TAP_MUTATIONs

- If datatype is not supported by connection, check
for the JSONness of data before setting the datatype.

Change-Id: I0e6d4af98af1c55b8e64df240036dd6ed13f870d
Reviewed-on: http://review.couchbase.org/38246
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>