Implement sentinel based DB capacity scaling

Implement sentinel based DB capacity scaling

For time being SDL has supported standalone DBAAS DB and DBAAS HA DB deployment
with Redis sentinel. With this commit extent SDL functionality to support Redis
sentinel based DB cluster where we have multiple DBAAS Redis sentinel groups
and these groups can be used to spread out SDL DB write and read operations to
different DB instances.
Implement cluster DBAAS DB service addresses reading from environment variable
'DBAAS_CLUSTER_ADDR_LIST'.
Implement crc32 hash value calculation from namespace string and selection of
a DB instance from DB cluster based on calculated hash.

Issue-ID: RIC-699

Signed-off-by: Timo Tietavainen <timo.tietavainen@nokia.com>
Change-Id: I8999c3c03d2d80d32a57d8ec051632b975bf9dc2