FIX: Check Mounted Root Catalog Hash Early

This adds the check for the mounted root catalog hash into `health_check()`. This way it is always ensured, that the release manager machine is operating on the newest version of the repository. However, I dropped the automatic remount in `cvmfs_server transaction`, since this is the wrong place to fix inconsistencies. In the bug found by ATLAS last week it didn't have any effect, since the transaction was not fully committed.

I believe, the `cvmfs_server` commands should not blindly try to fix inconsistencies but report them and fail gracefully. Anyway, what is actually the reason for pinning the CVMFS client on the server side to an explicitly specified revision? Wouldn't it be sufficient to remount it after an revision update and let it pick up the latest version?

Additionally this updates test case 536 to try out the new consistency check.

**Note:** This contains [Pull Request 538](https://github.com/cvmfs/cvmfs/pull/538).