Add an option for restricted migration
Add an option for restricted migration

This option will allow node evacuation with migrations only
off the nodes to be evacuated.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>

ganeti/ganeti,grnet/snf-ganeti,dimara/ganeti,apyrgio/snf-ganeti,bitemyapp/ganeti,leshchevds/ganeti,leshchevds/ganeti,dimara/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/ganeti,ganeti/ganeti,leshchevds/ganeti,yiannist/ganeti,mbakke/ganeti,ganeti/ganeti,bitemyapp/ganeti,apyrgio/snf-ganeti,mbakke/ganeti,yiannist/ganeti,mbakke/ganeti,onponomarev/ganeti,andir/ganeti,yiannist/ganeti,andir/ganeti,grnet/snf-ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti,andir/ganeti,apyrgio/ganeti