[api] allow engines not in our git to be loaded

They need to drop a file in lib/engines which requires the engine and
implements mount_it call
[api] add (disabled) test route for crash/errbit setup testing
[dist] sphinx db keeps becoming incompatible

it feels like every second update we run into crashes due to that.

So lets always wipe it, the re-creation time is short enough
[backend] write a line when send binary release tracking event in logfile
[api] fix "not()" operator in xpath queries

also adding search support for obsolete time
[ci] cleanup
[api] fix obsolete_time for new binary_release items
[api] qualität ist was bugfrei ist (free cite from Otto Rehagel)
[dist] do not fail without sphinx db
[backend] repair import handling if the old full handling is used

It got broken with commit #80090475.
[backend] put '--directdepsend--' marker before prereqs

Newer perl-BSSolv will look for that marker.
[backend] only add directdepsend marker if we have prereqs
[api] do not crash when refering to a not existing repository
[api] improve readability
[api] store also binary build time in tracking
[backend] put 'medium' in packtrack data for isos/repos
[api] report also operation on binary release search results
[api] support binary release search for operation

and fix xpath syntax for disturl and supportstatus
[api] run some delayed jobs in special queues

* bug issue tracker job runs in extra queue to avoid that an external slow
  bugzilla server is slowin down processing all jobs
* binary tracker is doing heavy SQL load, so limit it to one job
[backend] fix media to medium attribute for product pool repos