jenkins: make python default to python3

This change supercedes change 8124 and work done by Fathi.

The current jenkins image installys on python3, which
doesn't set a symlink for "/usr/bin/python".  This creates
problems as a lot of our support scripts are still calling
"python" in order to execute.

Instead of continuing to obscure the problem, let's force
the upgrade of python3 as the default and install some
of the python3 libs that will be needed.

Let's also take the time to upgrade to current versions
of jjb and python-jenkins.

Change-Id: I7257b34e48fc14fb4cd9940808582e7611d52121
Signed-off-by: Kelley Spoon <kelley.spoon@linaro.org>
1 file changed