Decoupled DC from Region

Priam is built based on the assumtion that C*'s notion of DC will
always be the AWS region. This limits use cases where we want to have
two Datacenters simulated in one AWS region for different purposes like
one being OLAP and another OLTP. There has been some work done on 1.1
with integration of DSE. This patch is not merged with DES changed, but
just addreses the coupling of DC and Region by separating their
definition in the IConfiguration. Furthermore, it uses a new
configuration parameter called dc_suffix (see CASSANDRA-5155) to emulate different DC
in the same AWS region. I did not add automatic propagation of
rackdc.properties file yet as some work was done in DSE branch and didn't
want to cause conflicts till that successfully merges with master.