parse-js, roundtrip-test.js: Set debugging flags with ParsoidConfig.

* Set debugging flags after creating the parsoidConfig object instead of using
env.conf.parsoid inside a callback function.
* Creates a function in mediawiki.Util.js to set the interwiki and apiURL flags
(common to parse.js and roundtrip-test.js), in addition to other templating and
processing flags.

Change-Id: I29694e6296ea9c8368a91aef511c63a176f8ad55