fix broken refs to salt.client.ssh.client.SSHClient

************* Module salt.modules.saltutil
salt/modules/saltutil.py:647: [E1101(no-member), _get_ssh_or_api_client] Module 'salt.client.ssh' has no 'SSHClient' member
salt/modules/saltutil.py:724: [E1101(no-member), cmd_iter] Module 'salt.client.ssh' has no 'SSHClient' member
************* Module salt.runners.manage
salt/runners/manage.py:207: [E1101(no-member), safe_accept] Module 'salt.client' has no 'SSHClient' member
Merge pull request #18697 from hulu/sshclient

fix broken refs to salt.client.ssh.client.SSHClient