Move imports to top-level

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Fix a circular import

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Ignore the exit code of ssh-keyscan

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Exempt teuthology-updatekeys from test_invalid

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Merge pull request #132 from ceph/wip-refactor-scripts

Fix imports; fix keyscan_check()