Improved setting of tracing flags in parse.js and roundtrip-test.js.

* Sets --htmlwt when --selser flag is set.
* Automatically enables --trace wts whenever --trace selser is set.
* Enables tracing flags in roundtrip-test.js.

Change-Id: I80a8a15bd6d3629613ee80744e8a28e127c44b38
Merge "Improved setting of tracing flags in parse.js and roundtrip-test.js."