virt: move disk tests into a sub-directory

The test_virt_disk.py, test_virt_disk_vfs_guestfs.py, and
test_virt_disk_vfs_localfs.py test cases were in the top
level nova/tests/virt directory. Current policy is to use
a directory location that matches the source being tested,
so they should be in either nova/tests/virt/disk or
nova/tests/virt/disk/vfs respectively. The test_loop.py
and test_nbd.py tests should be in nova/tests/virt/disk/mount
too. Finally fakeguestfs.py should also be kept in the
nova/tests/virt/disk/vfs directory

Change-Id: Iebee539d202d5122939ae478fd482f19b19f604d
virt: switch order of args to assertEqual in guestfs test

Policy is to have the expected data first in an assertEqual
call, so update the guestfs test suite to match.

Change-Id: Ic0cbe354dde87881ebaec78bb2cb03a32edd36c5
Set python hash seed to 0 in tox.ini

New tox (>=1.7.0) sets a random python hash seed by default. This is
generally good for testing because it will help keep projects working
regardless of the hash seed, but nova unittests don't currently pass
with a random hash seed so set it to the python default seed.

This change will allow us to use new tox again and remove the
restriction on tox<=1.6.1 to run unittests.

Redundant setenvs for specific test envs are removed to prevent them
from overriding the PYTHONHASHSEED value.

Note this change will need to be backported to the stable branches to
keep unittests there working with new tox as well.

Change-Id: Ib54364877a251db48c54dfdc43c503281ea1f04a
Merge "Set python hash seed to 0 in tox.ini"
Merge "virt: move disk tests into a sub-directory"
Merge "virt: switch order of args to assertEqual in guestfs test"