Skip data-request tests if disconnected from net.

Some of the current unit tests rely on an internet connection being
present to fetch data from remote issue-trackers.  More accurately,
only one test does this currently, but more integration tests are in
the works.

But people aren't always connected to the internet: people code in cars,
on planes, or outside.  It is rare, but I wanted to provide options for
people who want to run the test suite to check their work, but don't
have access to the internet.

This commit fixes this problem by adding guards around unit-tests to
prevent them from being run when not connected to the internet.  This
is done using unittest.TestCase's skipIf annotation.