Set version bounds for diskimage-builder

In an attempt to begin managing Ironic stable branches, we'll be moving our
DevStack testing toward relying on a versioned DIB dependency from pip instead
cloning and running from trunk.  This sets a version requirement to the most
recent DIB release.

Change-Id: If69963dba3cc55aa79bd0165ab147e7b3f776f75
Merge "Set version bounds for diskimage-builder"