Enhance the validation of the quotas update

Need check whether the already used and reserved exceeds the new quota
before update it.

DocImpact
Implements a validation to validate whether already used and reserved
quota exceeds the new quota when run 'nova quota-update', it will throw
error if the quota exceeds. This check will be ignored if admin want to
force update when run 'nova quota-update' with additional option
'--force'.
This validation help admin to be aware of whether the quotas are
oversold when they try to update quota and also provide an option
'--force' to allow admin force update the quotas.

Fix bug 1160749

Change-Id: Iba3cee0f0d92cf2e6d64bc83830b0091992d1ee9
Merge "Enhance the validation of the quotas update"