This provides a convenient way to start Karma tests and auto-run
them when test files are changed.

Because the test files are incorporated into a Browserify bundle
by karma-browserify which watches files for changes via watchify(),
we can turn off Karma's own watching of the test files.

This fixes a problem where changing a test spec file would result
in Karma running all the tests twice, once after the test spec file
changed and then again afterwards due to the browserify bundle
being updated a second or two after the test spec file changes.