NEW_USER_DEFAULT_INSTANCES names VMs, and a name may repeat across hosts.
A name with no VM, or with one on two hosts, made creating any user a 500.
The create form now looks the names up and says which one is not exactly
one VM; the user and its default VMs are saved together.
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.
