MasterRpcServices#getSecurityCapabilities explicitly checks for the HBase AccessController implementation

Sharmadha brought a failure to my attention trying to use Ranger with HBase 2.0 where the grant command was erroring out unexpectedly. The cluster had the Ranger-specific coprocessors deployed, per what was previously working on the HBase 1.1 line.

After some digging, I found that the the Master is actually making a check explicitly for a Coprocessor that has the name org.apache.hadoop.hbase.security.access.AccessController (short name or full name), instead of looking for a deployed coprocessor which can be assigned to AccessController (which is what Ranger does). We have the CoprocessorHost methods to do the latter already implemented; it strikes me that we just accidentally used the wrong method in MasterRpcServices.