ACCUMULO-3199 Internal refactor to add ClientContext

  This patch introduces a new ClientContext object that contains Credentials,
  Instance, and Configuration provided from the client API. This new object is
  passed around internally in place of the previous three objects. An
  AccumuloServerContext is also introduced, which extends the ClientContext.
  Together, these objects ensure the proper configuration, credentials, and
  everything else needed to communicate with other system components are
  available to any RPC-related code.

  These new object types also reduce the need to create multiple references to
  commonly used internal objects (such as HdfsZooInstance and
  SystemCredentials), and avoids storing information in static fields. As a
  side-effect, this should allow for better testing with mocked components.

  This fixes ACCUMULO-3252, and may lay some groundwork for ACCUMULO-2589.
ACCUMULO-3167 Decouple MiniAccumuloCluster from every integration test.

Use the more generalized AccumuloCluster and implement tests in terms
of an interface which is common across the deployment characteristics
of that cluster.
ACCUMULO-3167 First start at adding in ClusterControl to the StandaloneAccumuloCluster
ACCUMULO-3167 Get rid of the extra newline when we're trying to grab the pid
ACCUMULO-3167 Get the miniaccumulo cluster tests working again after introducing MiniAccumuloClusterControl
ACCUMULO-3167 Remove the notion of managed and unmanaged clusters; all clusters can be controlled.

Start trying to rework some of AccumuloClusterIT to be allow for more ITs
to run against an existing instance.
ACCUMULO-3167 Avoid running DynamicThreadPoolsIT against a real cluster for now.
ACCUMULO-3167 Start switching over some tests
ACCUMULO-3167 Implement stopAll and startAll in ClusterControl
ACCUMULO-3167 Pull back the log level
ACCUMULO-3167 Switch over CleanWalIT to clustercontrol
ACCUMULO-3167 Reuse the constructors
ACCUMULO-3167 Start the massive porting of ConfigurableMacITs over to AccumuloClusterIT
ACCUMULO-3167 Make DynamticThreadPoolsIT work against standalone
ACCUMULO-3167 Some extra logging in property-based configuration
ACCUMULO-3167 Port over some more ITs to the new test class
ACCUMULO-3167 Port over NoMutationRecoveryIT
ACCUMULO-3167 Add an exec to ClusterControl. Fix up ReadWriteIT.
ACCUMULO-3167 Include a nice log.info message for the command being exec'ed.
ACCUMULO-3167 Port over more tests to AccumuloClusterIT

Make sure tests don't destructively change the configuration.
Use table names which start with the test class name and method
so the base class can clean them up automagically.