Recovery tests were updated:

* recovery tests were slightly refactored
(it's easy to add new tests cases for both dc and merge recovery tests)
* tests with `--dump-file` and `--nprocess` options were added for
recovery-merge tests
`test_taken_time` was renamed to more correct `test_elapsed_time`
Merge pull request #78 from kis8ya/features/recovery-tests-update

Recovery tests were updated