The size of deployment_info grows as n^2 depending on
nodes number. That's because common_attrs, which is
merged into each node's contains info about all nodes.
For example for 600 nodes we store about 1Gb of data in
the database. So as first step let's store common_attrs
separately in deployment_info structure inside python
code and in the database.
Also removed old test for migrations, which are not related
to actual database state.
Change-Id: I431062b3f9c8dedd407570729166072b780dc59a
Partial-Bug: #1596987
7a83ee0cac