Fix username,password,host Jenkins vars
Fix username,password,host Jenkins vars

In all our other vCloud integration tests, the following envvars
are used:

* API_USERNAME
* API_PASSWORD
* API_HOST

Fixing up this instance so that it matches this convention

UKHomeOffice/vcloud-core,UKHomeOffice/vcloud-core,gds-operations/vcloud-core,gds-operations/vcloud-core