Add support for memory overcommit in live-migration

Override the live-migration memory check in FilterScheduler and
make it use RamFilter for checking available memory on target
host.

Resolves bug 1068258.

Change-Id: I3002b8330e595ce71e2718b2091d3b0b99747707
separate libvirt injection and configdrive config variables

This is mostly a refactoring so that if config drive is required,
variable lookup only needed for the injection case, is avoided.

There is a functional change here to make 'admin_pass' consistent
with the other variables in that the libvirt_inject_password flag
now does _not_ control whether the admin password is placed
in the config drive.

Change-Id: Ib79971aa050e56e5aa72fdd69aadd7539b2bd315
Merge "Add support for memory overcommit in live-migration"
Merge "separate libvirt injection and configdrive config variables"