Add unit coverage for parrableIdSystem getId callback

[icflournoy]

To keep my changes incremental I'm opening up this discrete PR that only adds better unit testing of the parrableIdSystem module. This PR and soon to come future PRs will merge into the parrableIdSystem/base branch which will then be opened upstream for review.

These unit tests also cover the newly added data.url property.

[icflournoy]

[icflournoy@thinkpad Prebid.js]$ time gulp test
[21:10:23] Using gulpfile ~/dev/Parrable/Prebid.js/gulpfile.js
[21:10:23] Starting 'test'...
[21:10:23] Starting 'clean'...
[21:10:23] Finished 'clean' after 35 ms
[21:10:23] Starting 'lint'...
[21:10:45] Finished 'lint' after 22 s
[21:10:45] Starting 'test'...
ℹ ｢wdm｣:
ℹ ｢wdm｣: Compiled successfully.

START:
ℹ ｢wdm｣: Compiling...
ℹ ｢wdm｣:
ℹ ｢wdm｣: Compiled successfully.
27 04 2020 21:11:19.634:INFO [karma-server]: Karma v4.4.1 server started at http://0.0.0.0:9876/
27 04 2020 21:11:19.635:INFO [launcher]: Launching browsers ChromeHeadless with concurrency 5
ℹ ｢wdm｣: Compiling...
27 04 2020 21:11:19.669:INFO [launcher]: Starting browser ChromeHeadless
ℹ ｢wdm｣:
ℹ ｢wdm｣: Compiled successfully.
27 04 2020 21:11:21.481:INFO [HeadlessChrome 81.0.4044 (Linux 0.0.0)]: Connected on socket b2_xv-eVfuZJQ7RHAAAA with id 20943311
INFO: 'sinon.reset is deprecated and will be removed from the public API in a future version of sinon.'
INFO: 'sinon.reset is deprecated and will be removed from the public API in a future version of sinon.'
INFO: 'sinon.reset is deprecated and will be removed from the public API in a future version of sinon.'

Finished in 5.392 secs / 3.219 secs @ 21:11:28 GMT-0400 (EDT)

SUMMARY:
✔ 5499 tests completed
ℹ 3 tests skipped
[21:11:28] Finished 'test' after 42 s
[21:11:28] Finished 'test' after 1.07 min

real	1m5.439s
user	1m12.078s
sys	0m1.764s

[ralejandre]

LGTM.