xenapi: Fix test_rescue test to ensure assertions are valid

The assertion in this test gathers the list of VDI references and then
checks if the string 'swap' isn't in the list. A VDI reference is a
UUID, so the string 'swap' will never match, even if the code being
tested is buggy.

Compare against an actual VDI reference. Also, add a positive assertion
to check that the root disk from the original VM is attached.

Change-Id: I3e3e9798ce63f2f260b7993620fde3749452bfc9
Closes-bug: 1290903
Make nova-network use conductor for security groups refresh

This makes nova-network use the existing conductor interface for
triggering security groups member refreshes.

Related to blueprint nova-network-objects

Change-Id: Ieca163d67cd005534acb225df83457d755295af9
Related-bug: 1290568
Block database access in nova-network binary

This mirrors the code we have in cmd/compute.py to wedge the database
module so that we can't add any more direct calls, and will highlight
any stragglers.

Related to blueprint nova-network-objects

Change-Id: Ib12415d84de950265626b4a804f33717203d9765
Related-bug: 1290568
Merge "xenapi: Fix test_rescue test to ensure assertions are valid"
Merge "Make nova-network use conductor for security groups refresh"
Merge "Block database access in nova-network binary"