Configuration options for error regex and log file in the config now

Making it possible for one to overwrite the default set of regexes
used to search for device block errors in the log file. Also making
the log file naming pattern configurable by setting them in the
drive-audit.conf file.

Updating "Detecting Failed Drives" section on the admin guide as well.

Change-Id: I7bd3acffed196da3e09db4c9dcbb48a20bdd1cf0
Merge "Configuration options for error regex and log file in the config now"