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)
for a clarity: the `mi` is a input parameter of common lambda `mi4ip` - one for 4x lambdas, it will used for "caching" also 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.);