core: Adds scheduled job DwhHeartBeat

Adds DwhHeartBeatInterval option to ConfigValues.
Adds scheduled job DwhHeartBeat that periodically updates dwhHeart
variable in dwh_history_timekeeping table.
DwhHeartBeatInterval is editable in engine-config.

Change-Id: Ib0db94681e678f10af40e2ffd3399231e0b8e421
Bug-Url: https://bugzilla.redhat.com/962177
Signed-off-by: Martin Perina <mperina@redhat.com>