Test for newlines in omero obj

[joshmoore]

see: ome/omero-py#279

Without this PR, no attempt to pass a newline to the obj command will succeed. e.g.:

omero obj update Dataset:123 description=$'A\nB'

or

omero obj update Dataset:123 description="A

B"

will stop at the A.

With this PR, both usages (and likely others) will correctly pass a newline to the server.

[will-moore]

Test is passing at https://merge-ci.openmicroscopy.org/jenkins/job/OMERO-test-integration/707/testReport/OmeroPy.test.integration.clitest.test_obj/TestObj/test_newlines/
LGTM 👍