There are 3 tests that cover the following cases:

1. single OFD lock
2. overlapped OFD locks
3. inhertited OFD locks

Tests logic is similar to logic of tests for other lock types.

OFD lock specific header-only library was added to avoid code
duplication in the tests.

travis-ci: success for series starting with [1/2] locks: Add ofd locks c/r
Signed-off-by: Begunkov Pavel <asml.silence@gmail.com>
Signed-off-by: Eugene Batalov <eabatalov89@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>