hnbgw: test PS RAB Ass both with and without PFCP

Add mp_enable_pfcp_tests. When true, osmo-hnbgw-with-pfcp.cfg needs to
be used.

Related: I39b9632f8524a9f3455c1a2d7611bfe8ba07c2fd (osmo-hnbgw)
Related: I02b60941343000a4618e95f56326bec170c32bfe (docker-playground)
Related: SYS#6093
Change-Id: I511e758807e0512c18f3f9e0a8c4699b9a3f5992
3 files changed