_error_in_logs function of driver.py shall check all nodes

1. Don't simply return, if one node is clean or not clean.
2. It's better to log all errors and return all errors.

Change-Id: Ib0e23bff013836347f90bed50dd1d3a9566e6bad
Close-Bug: #1229957
Merge "_error_in_logs function of driver.py shall check all nodes"