tools/run_pylint.py: Handle unforseen exceptions running pylint

In some testing scenarios, such as daily pylint checking
on py 2.4, we noticed the attempt to inspect some pygtk
code generated problems such as:

RuntimeError: could not open display

Making the rest of the checks to be aborted. Let's handle
the exceptions and print the messages as we should.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>