The newly released pylint version 2.2.0, changed its default behavior
(enabled) the following checks:

 * :unnecessary-pass (W0107): *Unnecessary pass statement*
   Used when a "pass" statement that can be avoided is encountered.

 * :unused-import (W0611): *Unused %s*
   Used when an imported module or variable is not used.

Let's apply fixes to those checks, and at the same time, pin the
pylint versions so that our CI environment is more stable (code that
test our code -- pylint -- doesn't change, while our code changes).

For Python 2, the latest release was 1.9.3, so let's use that.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

The skip() method has been deprecated for quite some time.  Let's
remove it for good and have users using the decorators and cancel()
instead.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

self.skip() is to be deprecated. This is the first step, adding a
message to the exception raised by the self.skip() and adjusting the
examples tests accordingly.
Signed-off-by: NAmador Pahim <apahim@redhat.com>