Add hints to what the Migration attribute values are
Add hints to what the Migration attribute values are

Knowing the difference between dest_compute and dest_host
always requires looking at where it's set in the code (the
ResourceTracker during a move claim). This change simply adds
some comments to those source/dest attributes about what they
are.

Change-Id: I01bf5266127db41b4b1d5cfd010e38c2a09602c5

mikalstill/nova,mahak/nova,openstack/nova,phenoxim/nova,gooddata/openstack-nova,mikalstill/nova,klmitch/nova,klmitch/nova,rahulunair/nova,klmitch/nova,mahak/nova,gooddata/openstack-nova,phenoxim/nova,gooddata/openstack-nova,klmitch/nova,rahulunair/nova,mahak/nova,openstack/nova,mikalstill/nova,gooddata/openstack-nova,openstack/nova,rahulunair/nova