build_requestv2: Extract common code to base class
build_requestv2: Extract common code to base class

Preparation for a new request class

* OSBS-8040

Signed-off-by: Martin Bašti <388356a3851efe39ff0604de6d8fb2e16e10a0b7@redhat.com>

projectatomic/osbs-client,projectatomic/osbs-client