Multiple DBAAS Redis Sentinel groups

Added support to have one or more Redis Sentinel DB groups. The DB groups can
be used to spread out SDL DB operations to different DB instances. The new
DBAAS_CLUSTER_ADDR_LIST environment variable is used for Sentinel DB service
addresses configuration. The selection of DB instance is done based on the
calculation of crc32 value from the namespace string and return modulo hash
value of number of addresses in the list.

Issue-ID: RIC-699

Change-Id: I8bb3a78680cedfba4a39f06f7e2f8cdd60d26949
Signed-off-by: Petri Ovaska <petri.ovaska@nokia.com>