Additional date/time formats for datedetector testcases

Also made a note that some workarounds for certain date/time formats
may cause week/year day to be incorrect. This does not affect
functionality of fail2ban so no urgency to fix.
Correct datedetector testcases for TAI64N format
Merge branch 'datedetector-testcase' of https://github.com/kwirk/fail2ban

* 'datedetector-testcase' of https://github.com/kwirk/fail2ban:
  Correct datedetector testcases for TAI64N format
  Additional date/time formats for datedetector testcases
DOC: reverted unneeded stripping of DoW + added comments for why [:6]