Merge branch 'devel-2.1'

* devel-2.1: (22 commits)
  NEWS: fix empty lines
  Fix a unittest name and docstring
  Force ssh to allocate a tty
  Fix a unittest docstring
  IsProcessAlive: retry stat() a few times
  Retry{Again,Timeout}: explain reraising
  utils.Retry: pass up timeout arguments
  Add a few Retry unittests
  Bump version for 2.1.2.1 release
  Update NEWS for Ganeti 2.1.2.1
  KVM: only export instance tags if present
  ssh.GetUserFiles: move to EnsureDirs
  Hypervisors: use utils.EnsureDirs
  backend: remove a couple of useless mkdir calls
  daemon.GenericMain: fix docstring
  jstore: use EnsureDirs, and add more constants
  Bump version for 2.1.2 release
  Update NEWS file for 2.1.2
  Add dates to the NEWS file
  RAPI QA: Test instance creation/removal via RAPI
  ...

Conflicts:
	NEWS
	  - trivial (merge NEWS entries)
	lib/backend.py
	  - trivial (master doesn't have the changed code)
	lib/constants.py
	  - trivial (merge constants, plus one s/0700/SECURE_DIR_MODE/)
	test/ganeti.utils_unittest.py
	  - trivial (name+docstring changes)

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>