Move timezone tests to integration test.

Interacting with timezones will result in checks against the filesystem.
This access, by definition, is an integration test.  Creating a
*integration_test.go file will signify this change.

When interacting with Travis-ci.org, the ubuntu boxes plus go 1.1 do not
seem to support shortcode timezones, think PST.  In this case, the tests
are skipped.  This is not ideal, but the IRC #go-nuts channel has
indicated timezone support is still lacking.  We should advise users of
hugo that timezone support may be an issue and report any odd behavior.
The workaround is to use numeric timezones (-08:00 for PST, etc.)