Add script debugging options

[zultron]

Add two environment variables that may be defined with docker run -e
to aid debugging:

• Define $DEBUG_TRACE to turn on init-data and
  ipa-server-configure-first script tracing

• Define $DEBUG_NO_EXIT to disable container exit after failures

[adelton]

The $DEBUG_TRACE part LGTM.

As for the $DEBUG_NO_EXIT, would it be possible to do it without touching /usr? Eventually we want to be able to run the container read-only, so /etc might be better here. I also wonder if addressing it in systemd-poweroff.service.d/ might be more appropriate than in the individual user services -- you could start something like sleep infinity there.

[zultron]

@adelton, you're right, I should have used systemd unit drop-ins from the beginning. Take a look at the revised PR.

I ended up sticking with adjusting the FailureAction in ipa-server-*.service. With ExecStartPre=sleep infinity in the systemd-poweroff.service unit, other units get killed, so it's harder to reproduce the failure environment.

Thanks for the review.

[adelton]

Untested but looks good to me.

[felipevolpone]

@zultron thanks for the patch. I'm kind busy right now, but I'll find some time to test it this week and then, merge it.

[felipevolpone]

Tested and it works properly. LGTM.
Do you see any restriction here @stlaz ?

[stlaz]

Tested both the env. variables and they really work great. Thanks!

[adelton]

Note, in #219 I now propose to put the overrides to /run/systemd, to avoid polluting /data.