Improve web tests

[kingosticks]

During review/testing of #287 I realised there's a potential problem with the way we mix relative and absolute URLs when using the web client when it comes to trying to clear specific parts of the cache. So I wanted to be a lot more explicit in the tests and and have the URLs we use more closely match reality. This will be helpful for the PR that addresses this issue.

Plus a fix I had been sitting on for a while which uses the skip_refresh_token in the other places it's useful (rather than directly messing about with numbers).

[codecov]

Codecov Report

Merging #298 (d04787e) into master (790b7b7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #298   +/-   ##
=======================================
  Coverage   96.68%   96.68%           
=======================================
  Files          13       13           
  Lines        1206     1206           
=======================================
  Hits         1166     1166           
  Misses         40       40           

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