Make block devices mounts permanent within service instances

Restart of service VM does not save mount state of block device for share.
So, if we do not restart m-shr we have export to dir that links not to
block device, but to root filesystem of service VM.

Changes:
- added sync method of temp and permanent fs mount files;
- changed lock value for mount operations from share id to service instance id,
  because any action changes common config file;
- updated related unittests;

Change-Id: I874d84f5342208906379aba5572540a984f79f03
Closes-Bug: #1367731
Merge "Make block devices mounts permanent within service instances"