Description of problem:
when updating a cost model, the cost numbers become only updated back to the first of the current month

Version-Release number of selected component (if applicable):
current version


Steps to Reproduce:
1. open cost models page, select/open a cost model
2.change a cost models rate from Metric = CPU & Measurement = Request (core-hours) to Metric = memory & Measurement = Request (GB-hours) 


Actual results:
numbers in cost explorer do only get updated with the results of the changed cost model until the 1st of the current month.


Expected results/behavior:
when changing a cost model an additional dialog should appear which allows to define a date in the past (a date before the first of the current month)  until which the cost data should get updated with the new cost model rule set/calculations