jstest: add the ability to skip unit tests

To use, just | throw SkipTest(reason); | from the test.  The reason is
optional.

(integrated from komodo (trunk) change 81269 by marky)

git-svn-id: http://svn.openkomodo.com/repos/openkomodo/trunk@13377 b87d16e7-d29f-4ee1-b5ec-817d645d335f