Stay `set +e` in the test masked that this test has apparently never
worked in the first place: when a unit is killed with a signal, any
bound unit is stopped retroactively via
retroactively_stop_dependencies() but it's not restarted again, as the
restart for the bound unit is queued as TRY_RESTART in a following
transaction - but at this point the bound unit is already inactive, so
the TRY_RESTART job collapses into a NOP.
Let's account for this and also add a couple of test cases for
RestartMode= with an explicit restart, which should trigger the bound
unit as well (assuming it's active).
Follow-up for 9b42c58a2b.
Frantisek Sumsal
2c4e86c290