cfg.base: Add migration relative parameters.

Use remote_ip and local_ip as destination and source host
for migration may disturb libvirt tests. So separate them
only for migration relative tests.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #1732 from yumingfei/migrate_parameters

cfg.base: Add migration relative parameters.