ATMO-291 Remove unused import of service.allocation.
	modified:   api/instance.py
ATMO-291 Add logic to apply time period based allocation.

* time_period is a relativedelta python object. months=1 parameter
  implies monthly time period allocation. day=1 parameter is the
  day of the month to reset time period allocation.

	modified:   service/allocation.py
	modified:   service/instance.py
Merge branch 'atmo-291' into gunnr