[cfg01] Reduce mine_interval to 15 min

[cfg01] Reduce mine_interval to 15 min

Some PODs are fast enough to get past installing, syncing and using
MaaS to provision the OS on the baremetal nodes before the 1h mine
refresh.

Since mine.update operation is fast enough to go unnoticed and we
only collect IP addresses, grains and pem entries, schedule it every
15 minutes.

Due to reclass class inheritance, we can't easily override this via
pillar data, so handle it via entrypoint.sh.

Change-Id: I0d8ed2da838ad09c94e9327d0131d3e239de4f08
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>