Describe the --restricted-migration option
Describe the --restricted-migration option

Add the --restricted-migration option to the man page together with
a hint on the intended use case.

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

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