CBIDXT-59 Storage Format for Secondary Key/Value

Change-Id: Idcb3f6ec777e370b6e3221967362bb062cd97012
Reviewed-on: http://review.couchbase.org/38142
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Tested-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>