Merge branch 'devel-2.5'

* devel-2.5: (24 commits)
  LUInstanceCreate: Release unused node locks
  htools: rework message display construction
  hbal: handle empty node groups
  Document OpNodeMigrate's result for RAPI
  Ensure unused ports return to the free port pool
  Re-wrap a paragraph to eliminate a sphinx warning
  Fix newer pylint's E0611 error in compat.py
  Fail if node/group evacuation can't evacuate instances
  Update init script description
  LUInstanceRename: Compare name with name
  LUClusterRepairDiskSizes: Acquire instance locks in exclusive mode
  Update synopsis for “gnt-cluster repair-disk-sizes”
  Move hooks PATH environment variable to constants
  Check the results of master IP RPCs
  Add documentation for the master IP hooks
  Add master IP turnup and turndown hooks
  Add RunLocalHooks decorator
  Generalize HooksMaster
  Update NEWS for 2.5.0~rc4
  Bump version to 2.5.0~rc4
  ...

Conflicts:
	NEWS
	doc/hooks.rst
	lib/backend.py
	lib/cmdlib.py
	lib/constants.py

Signed-off-by: Andrea Spadaccini <spadaccio@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>