[Support/LockFileManager] Make the LockFileManager more robust against races.

There was a race where:
- The LockFileManager tries to own the lock file and fails.
- The other owner then releases and removes the lock file.
- The LockFileManager tries to read the owner info from the lock file but fails now.

In such a case have LockFileManager try to get ownership again, instead of error'ing out.

llvm-svn: 203138