HBASE-12680 Move signal related code from ClusterManager to HBaseClusterManager and change ClusterManager to an interface

Summary: The reason of this change is to make us write implementation of ClusterManager not using ssh/unix signals.

Test Plan: The compilation is OK.

Reviewers: eclark, manukranthk

Differential Revision: https://reviews.facebook.net/D30201

Signed-off-by: Elliott Clark <eclark@apache.org>
HBASE-12683 Compilation with hadoop-2.7.0-SNAPSHOT is broken
HBASE-12692 NPE from SnapshotManager#stop (Ashish Singhi)
HBASE-12675 Use interface methods in shell scripts (solomon duskis)
HBASE-12685 TestSplitLogManager#testLogFilesAreArchived sometimes times out due to race condition
HBASE-12651 Backport HBASE-12559 'Provide LoadBalancer with online configuration capability' to branch-1
HBASE-12686 Failures in split before PONR not clearing the daughter regions from regions in transition during rollback (Vandana Ayyalasomayajula)
HBASE-12348 preModifyColumn and preDeleteColumn in AC denies user to perform its operation though it has required rights

Signed-off-by: Andrew Purtell <apurtell@apache.org>
HBASE-12696 Possible NPE in HRegionFileSystem#splitStoreFile when skipStoreFileRangeCheck in splitPolicy return true(Rajeshbabu)