automat _visualize.py code depends on both twisted and graphiz modules.
This patch fixes the condition where some tests were not skipped due
to twisted not being installed, but graphviz was.
Gentoo-bug: https://bugs.gentoo.org/665554
Upstream-PR: https://github.com/glyph/automat/pull/125
Package-Manager: Portage-2.3.99, Repoman-2.3.22
Signed-off-by: Brian Dolbec <dolsen@gentoo.org>
