Re-enable -1 child limits for nested quotas

Re-enable -1 child limits for nested quotas

Add back support for -1 limits of child projects. The way that we
support the -1 child limits requires the following changes:
  * Continue quota validation up the hierarchy if the current limit is
    -1 until we hit a hard limit or no more parents, and update the
    any relevant parents' allocated value along the way
  * When updating limits, special care needs to be taken when updating
    child limit to be -1, or when changing from a -1 limit
  * Enable support for creating reservations for "allocated" values
    to support the scenario that:
      - a volume is created on a project with a limit of -1
      - the parent's allocated value has been updated appropriately
      - the volume create fails and the child's in_use quota rolls back
      - now we must also rollback the parent's allocated value

NOTE: There is a race condition between validation the NestedQuotas
and when the driver may be switched into use, and if -1 quotas are used
the validation could be out of date. Will look into better support for
switching on of NestedQuotas on live deployment with -1 limits, which
would likely leverage the "allocated" reservation system.

Closes-Bug: #1548645
Closes-Bug: #1544774
Closes-Bug: #1537189
Change-Id: I2d1dba87baf3595cc8f48574e0281ac17509fe7d