Detect pseudo-distributed Llama cluster

Since we're no longer using the MiniLlama, we need to explicitly set
whether or not the cluster is pseudo-distributed. Impala needs this
information to correctly translate datanode addresses to a format that
Llama understands.

This change (adapted from one made by Casey) adds a method to the
frontend (callable via JNI) to get a configuration value from the Hadoop
configuration. We'll set that configuration value for local RM testing.

Change-Id: Ifd51db98a993ac0270dac2b832babbc394483c1a
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2549
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2754