Automate the current manual pybootchart tests. This includes a check
for the cairo dependency, skipping the test if appropriate.
Based on original patch from Armin Kuster <akuster808@gmail.com>
(From OE-Core rev: ff5370a381a4996b7da56aaaa7055f7a1786c823)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>