core: Fix async tasks insertion to include time zone info

Similar to other places (i.e - audit log insertion - log_time field)
We should insert the "started_at" time with time zone information

Change-Id: I06d2daaf5647d850c1c3a86f0610bf12a60c4ffd
Signed-off-by: Yair Zaslavsky <yzaslavs@redhat.com>