Catch instances less than zero error

This change prevents the number of App instances being set to a negative
number
Cloudcontroller can send job information with full urls (rather than just paths)

Signed-off-by: Phan Le <ple@pivotallabs.com>
Merge branch 'instances_error' of https://github.com/bravera/cloud_controller_ng

Conflicts:
	spec/models/runtime/app_spec.rb