More robust ThroughputProfileHandler GitLab replies

If the test is run for a lhcb-master-ref slot, it could be necessary to generate replies for multiple -mr slots.
e.g. When two ci-test commands are launched quickly after one another and share the same -ref slot, the -ref slot could finish after both -mr slots.
In this case the -ref slot needs to generate replies for both of the -mr slots.

Thanks to @rmatev for catching this corner case and suggesting a nice workaround :)

This MR now implements that a -ref build queries all related -mr builds and sends replies for all of them.
Also included an extra commit running lb-format on this python file to make it a bit cleaner.