Updated usage of locks

Changes:
- replaced direct usage of sychronized func from lockutils with local wrapper,
  that provides prefix;
- 'lock_path' is not provided anymore as hardcode, defined 'lock_path'
  in config is expected;
- added MANILA_LOCK_PATH to devstack plugin, to be able to set path
  before installation.

Change-Id: I6518df0a6d32f1021b19a48f928f9ec8b00140b2
Closes-Bug: #1347915
Merge "Updated usage of locks"