A tombstone kept the VM's name and UUID but not its compute, so the page
could not say where the VM had been. It now stores the compute's name (as
text: the compute may be the one deleted) and the list shows it; records
made before this have no host. Deleting a record says so, and the admin
tables use scope="col" instead of the invalid span="col".
Closes#217
131 test modules sat next to the code they test; instances alone had
51 of them beside views.py and utils.py. They move into a
tests/ package per app, and the JavaScript checks into
webvirtcloud/tests/js. Each non-empty tests.py becomes tests/test_views.py;
the empty generated stubs are removed.
Imports of the app's own modules become absolute, paths built from
__file__ go one level up, the live helper is instances.tests.livetest,
and coverage omits */tests/*. The suite discovers the same 960 tests as
before.
