inspektor: Add style checker

Use python-pep8 to point out style non compliances. This initial
commit implements only the style checker, the style fixer is yet
to come.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Add inspektor.style logger
inspektor.cli.app: Add style subcommand

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>