purge test domain for smoke / diff tests

[tripodsan]

before starting the tests, it should probably be best to purge the cache for the entire test domain.

[kptdobe]

I do not think this is enough here (purge only one url) but for the record:

Chai HTTP depends on the methods module which defines the purge method. In tests, you can simply run:
await chai.request(host).purge(path);
which sends a PURGE request. Pretty useful to purge a page before running a test on it.

[tripodsan]

I rather thought of purging the entire domain using the fastly api