Actually correct use of label.providers dict
Actually correct use of label.providers dict

* nodepool/nodepool.py: Commit 00514fc addressed inconsistent yet
working uses of the label.providers dict, but did not correct the
actual broken one. Take care of it now.

Change-Id: I2af44f5771dbb2d776cbce58c5e248d3fbfe24fb

seandst/nodepool,citrix-openstack/nodepool,Tesora/tesora-nodepool,Tesora/tesora-nodepool,seandst/nodepool,citrix-openstack/nodepool