Loosen anyjson dependency to avoid clash with ceilometer

Loosen anyjson dependency to avoid clash with ceilometer

Ceilometer depends on anyjson 0.3.1, whereas cinder requires
exacly 0.2.4.

The net effect is a devstack with ceilometer installed will
appear to work initially, as ceilometer is sparked up after
cinder. However, if any of the cinder services are subsequently
restarted, they fail with:

  pkg_resources.DistributionNotFound: anyjson==0.2.4

By simply allowing the cinder anyjson dependency version to
be greater than as opposed to an exact match, we can avoid
the clash.

Change-Id: I21737a2504705f15dd16e6762b44624678177442