test_otp: do not use paramiko unless it is really needed
    
    paramiko cannot be used in FIPS mode. We have few tests that import
    generic methods from test_otp (add_token/del_token) and those tests fail
    in FIPS mode due to unconditional 'import paramiko'.
    
    Instead, move 'import paramiko' to the ssh_2f() helper which is not used
    in FIPS mode (the whole SSH 2FA test is skipped then).
    
    Related: https://pagure.io/freeipa/issue/9119
    
    Signed-off-by: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Francisco Trivino <ftrivino@redhat.com>