virttest.libvirt_network_unittest: Fix method valid only on py >= 2.7

Use a more generic method, that will work in older
python implementations.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest unittests: Fix method valid only on py >= 2.7

Use older constructs that will make the tests possible
to work on older python versions.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest.utils_conn: Fix wrong arguments passed to exception

According to the constructor of ConnPrivKeyError, such
exceptions should be passed a key file and a stderr.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
virttest.utils_conn_unittest: Fix method only valid on py >= 2.7

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #1249 from autotest/more-pylint-fixes

More pylint fixes