Filters are supposed to be pluggable, but they are not, since you have
to modify __init__.py.
This adds a --scheduler_availabile_filters setting which replaces the
hardcoding in __init__.py. This setting is a MultiStr (a list, which
you can specify more than once) containing the full paths to filter
classes to make available to the scheduler. Using a value of
'nova.scheduler.filters.standard_filters' maps to all standard filters
included in nova under nova.scheduler.filters. This is the default
setting and matches what was in __init__.py before.
Also renamed --default_host_filters to --scheduler_default_filters to
make the flag a bit more clear.
Change-Id: I10eb54e9982b6d42316adfb2cc2600b44a9c3bdf
3f42e11ca0