The nova scenarios BootServerAttachCreatedVolumeAndLiveMigrate,
BootServerFromVolumeAndLiveMigrate, BootAndLiveMigrateServer are using
rally's own function to find a suitable target compute host for live
This function does not support all filters that are available and
configured in nova. This function only filters computes on AZ level.
For example it completely ignores flavor-aggregate mappings
(AggregateInstanceExtraSpecsFilter). This leads to wrong target host
selection and thus a failing live migration.
This patch removes the function _find_host_to_migrate and the argument
target_host that was given into the function _live_migrate.
This leaves the target host selection completely up to nova,
for live migration, which allows to benefit from the whole nova
scheduler filters implementation, to find a suitable host.