Fix divergence in attach_interfaces extensions

I pointed out in revision 7 of Ibe4cbd025700aa0d73a6d4d19fbf8f0005509428
that it we shouldn't use a different variable name in the identical code
shared between the v3 and v2 extensions, but that was never fixed before
merging.

Change-Id: I7c2853db2cbad30a37efd98947ebe687b37bfbe8
xenapi: Speeding up more tests by switching to NoDB

nosetests nova/tests/compute/test_compute_xen.py
          nova/tests/virt/xenapi/image/test_bittorrent.py
          nova/tests/virt/xenapi/image/test_glance.py

BEFORE: Ran 13 tests in 3.435s
AFTER: Ran 13 tests in 0.374s

Change-Id: I00cc990dab3f9af2c19aa57b84817fafc1cb01e9
Merge "Fix divergence in attach_interfaces extensions"
Merge "xenapi: Speeding up more tests by switching to NoDB"