`root_gb=0` indicates that a disk-resize shouldn't occur which is not
something that a default flavor should have enabled. This is
especially true of one named 'tiny' since the unresized image could
potentially be very large, leading to the unexpected result of a
'tiny' instance consuming a massive amount of disk.
The no-resize behavior is still supported, so if it's being relied on
for testing, additional, non-default flavors can still be created that
enable it.
DocImpact
Fixes bug 1175383
Change-Id: Ifa5827c7f87dae95214bc4a585adce5735a05d83
Rick Harris