Fix none getattempt lambda

fix-none-getattempt-lambda is a cherry pick from #716, that fixes:
- a bug from #838 (see https://github.com/fail2ban/fail2ban/issues/838#issuecomment-60904420)
- a fix for disturbing "bug" within servertestcase - preventing to write into stderr (see https://github.com/fail2ban/fail2ban/pull/716#discussion-diff-14126349)
- the `mi` parameter of common lambda `mi4ip` used also for "caching" inside `actions.__getBansMerged`, so it prevent to call a `database.getBansMerged` again, if it was already executed once for this ip/jail (so more performant and without lock/context switch etc.);
- <blockquote>and any other errors would raise an exception anyway.</blockquote>Yes, but this error will be catched inside of `actions.__getBansMerged` and just returns a ban ticket (although without merged info, but also without error), so banning will executed always;
- it is possible not applicable, but this error occurred often within, so I had fixed it there;
we should not build a new sources of error (I hope sometime this branch is in master - you guys are really too conservative for me:)