Description of problem:

Provisioning vm by changing the flavors using service dialog does not work.
The flavor change value does not get override.

Version-Release number of selected component (if applicable):
5.7.4.0.20170913182424_63a1e18

How reproducible:
100%

Steps to Reproduce:
1. set tenant quota for storage.
1. Create a service dialog with field: instance_type
2. Attach that dialog to catalog item
3. Order the service by changing the flavor from the dropdown list.

Actual results:
Provisioning with flavor/instance_type using service dialogs does not work.The changed flavor value is not considered in quota calculations.

Expected results:
Provisioning with flavor/instance_type using service dialogs should work

Additional info: