test: test `util` rather than `common`

test-sys.js tests common.inspect() (which is test-specific code) and not
sys (which, although deprecated, should still be tested).

This commit moves the tests to the not-deprecated util and adds a test
to check that deprecated sys and util are the same.

PR-URL: https://github.com/nodejs/node/pull/3256


Reviewed-By: Evan Lucas <evanlucas@me.com>