autobuild: allow AUTOBUILD_FAIL_IMMEDIATELY=0 (say from a gitlab variable)

autobuild: allow AUTOBUILD_FAIL_IMMEDIATELY=0 (say from a gitlab variable)

This allows making a push to do a full test ignoring errors without
needing "HACK!!!" commits on top.

Use like this:

git push -o ci.variable='AUTOBUILD_FAIL_IMMEDIATELY=0'

RN: Samba CI runs can now continue past the first error if AUTOBUILD_FAIL_IMMEDIATELY=0 is set

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14841
BUG: https://bugzilla.samba.org/show_bug.cgi?id=14881

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Michael Adam <obnox@samba.org
Reviewed-by: Noel Power <npower@samba.org>
[abartlet@samba.org backported from commit b81f6f3d71487085bb355392ce7f8eff2db5bb4d
 due to changes in 4.15 and later for the autobuild dependent jobs work
 that avoids rebuilding Samba in each task]

Autobuild-User(v4-14-test): Jule Anger <janger@samba.org>
Autobuild-Date(v4-14-test): Thu Sep 23 08:54:03 UTC 2021 on sn-devel-184

(cherry picked from commit f53c532c2292d07ab3374920bd83c1266663038e)