updating tests to remove test.gov.uk

Now using dev.gov.uk as per https://github.com/alphagov/plek/blob/master/CHANGELOG.md
updating whenever call to include govuk_setenv
updating whenever call to include govuk_setenv
Revert "updating whenever to inc govuk_setenv"

This reverts commit 3f3e3c54e3adb8a050259339759cff4d3ea8686d.
updating jenkins to use govuk_setenv
use GOVUK_WEBSITE_ROOT instead of Plek#find('www')

From Plek 1.0, Plek can no longer return URLs which aren't of the form
<app>.$GOVUK_APP_DOMAIN. Plek.current.find('www') is used by panopticon
to generate user-visible URLs - ie in prod it needs to be
https://www.gov.uk, while in preview it needs to be
https://www.preview.alphagov.co.uk.

The environment variable GOVUK_WEBSITE_ROOT is now provided to fill the
role that Plek.current.find('www') used to play.
Set sensible defaults if ENV vars are not found
Remove govuk_setenv we don't need it here
Lock plek to 1.0.0 as per our guides
Better regex escaping
Remove commented out line
Merge pull request #52 from alphagov/bump-plek-rebased

Bump plek rebased