Refactor AWS::EC2::Instance delete handling

Refactor instance to use the nova_utils delete function.

Closes-Bug: #1329453
Change-Id: Ie84fb3c5c9f6381e4eea3a5e99d62266a8abd023
Reusing PARAMETER_CONSTRAINTS value

The variable PARAMETER_CONSTRAINTS is not used, also this variable
makes code a little confused, because according to documetation
constraints for parameters don't include MIN, MAX and CONSTRAINTS
definitions. This patch makes this definition clear.

Change-Id: I47b49e3ed23720ed652f688f2901ae9bc6b01632
Merge "Reusing PARAMETER_CONSTRAINTS value"
Merge "Refactor AWS::EC2::Instance delete handling"