recovery: build secondary index in hot standby mode

End recovery (which means building secondary indexes) just after
last known log file was read. This allows fast switch to hot standby
instance without any delay for secondary index to be built.
Due to engine_end_recovery carryover, xdir_collect_inprogress,
previously being called from it, is now moved to garbage collector.

Closes #4135

(cherry picked from commit 5aa243de)