fuel-library: mysql: Fix spurious install timeouts

fuel-library: mysql: Fix spurious install timeouts

Backport the following fuel-library fixes from Fuel 9.1:
- wrong relationship in clusters mysql manifest
- Rsyslog doesn't have write permission to /var/log/mysql/ directory

These two bugs manifested as:
- random deploy issues waiting for MySQL to sync, without the server
  being installed;
- no MySQL logs were saved due to permission issues;

Closes-bug: ARMBAND-78

Change-Id: I317e45d013229145e2ccbd8bb4f76ae03d544098
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>