Removed reimport in models.py
Removed reimport in models.py

In trove/extensions/mgmt/instances/models.py, trove.instance.models
was imported twice, as different names.

TrivialFix

Change-Id: I30da8fc3587c8c705da05e7af699a277f544eac2

hplustree/trove,openstack/trove,openstack/trove,zhangg/trove,hplustree/trove,zhangg/trove