This allows users to create pipeline triggers that provide expanded
debug information in reports. This includes not only the debug
info currently available with the project-pipeline-config "debug" flag
(which includes decisions about running jobs), but additionally includes
information about why the change may not have been enqueued (and in
these cases, we will exceptionally report a non-enqueued item in order
to get this information to the user).
The intended workflow is:
1) User approves change
2) User is baffled by why change does not appear in pipeline
3) User leaves a comment with "gate debug" or a similar label/tag/etc
4) Zuul reports with a comment indicating why it was not enqueued
(depends on abandoned change, etc).
To make this more useful, the pipeline manager will now add several more
bits of information to the "warnings" list for non-enqueue conditions.
Also, the canMerge methods of the connections may now return a
FalseWithReason so their reasoning may end up in these messages.
Tests of this are added to each of the 4 code-review systems since the
attribute is set on the trigger itself, which is driver-specific.
These tests add coverage of the parsing and also exercise the canMerge
method. The Gerrit driver test includes several more variations to
exercise each of the new points in the pipeline manager that can
report a non-enqueued item.
While the git, timer, and zuul drivers also support this for completeness,
testing is not added to them since it is unlikely to be used.
Change-Id: Ifa59406bda40c2ede98ba275894b4bd05663cd6c
8c804042fb