Replace deprecated method ``testtools.try_import``

The method ``testtools.try_import`` was removed in testtools 2.8.1
in [1].

[1]https://github.com/testing-cabal/testtools/commit/1ac2d55ffb61f46b8f0496347dba926a8c24b2d4

Signed-off-by: Rodolfo Alonso Hernandez <ralonsoh@redhat.com>
Change-Id: I717ee29e41971eda79b5d226652bfa0f8b455fc3
2 files changed