Perform nodetool flush on 1:* keyspaces

This feature is a first step toward enhancing to perform more management tasks for a cluster.

##Configuration
To flush specific keyspaces, create FP “Priam.flush.keyspaces” and provide a comma delimited list of values (e.g. pappyperftest,dse_system).

If no FP exist, all kespaces (EXCLUDING system) will be flushed.

To specify interval, create FP “Priam.flush.interval”. The value is a name=value where “name” is an enum of hour, daily.
*hour means the flush will run at every hour. The value is an integer representing the minute. E.g. hour=0 will run on the hour, every hour.
*aily means the flush will run once daily at specified time. The value is an integer representing the hour. E.g. daily=10 will run at 10:00 a.m. daily.

##Manually invocation
curl “http://localhost:8080/Priam/REST/v1/cassadmin/flush”.
The result will be a json payload.
*For success, the payload is a list of keyspace(s) flushed. E.g. {"keyspace_flushed":["dse_system","pappyperftest","system_traces"]}
*For failure, the payload will be {“status:ERROR”, “component:flush”}