Synchronise how branches are specified in QPC and VPC #1941
Description
Currently in VagrantPlaybookCheck we specify a branch in the REPOSITORY_URL with e.g. https://github.com/sxa/openjdk-infrastructure/tree/mybranchname whereas in QEMUPlaybookCheck there is a separate INFRA_BRANCH parameter (Same for BUILD_BRANCH). We should make both behave the same way for a consistent user experience