Deleting this print_error results in the module exiting silently when login isn't possible unless VERBOSE = true:

<pre>
msf  auxiliary(mysql_hashdump) > run

[*] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed
msf  auxiliary(mysql_hashdump) > set VERBOSE true
VERBOSE => true
msf  auxiliary(mysql_hashdump) > run

[-] Unable to login from this host due to policy
[*] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed

</pre>

Not sure if this is the best approach (the module finishing silently on error and verbose = false)... awaiting for confirmation before merge.