VOLTHA 1.x 'atests' for bbsim not working

VOLTHA 'atests' seems to be not working using VOLTHA 1.x and latest BBSim.  Steps for reproducing:

• Build VOLTHA 1.x and BBSim containers locally using 'master' branch
• $ cd voltha/tests/atests/common
• $ ./run_robot.sh jenkinstest bbsim

There are at least two issues:

• The ONUs make it to DISCOVERED state but do not transition to ACTIVE.  Though BBSim is also being tested with VOLTHA 2.x, it seems that we're mainly testing tag `:voltha-2.1` and not `master` so that may be worth looking into.
• The DHCP test will fail if it makes it that far.  BBSim now waits for the dataplane flows to be pushed before starting the DHCP client, so the test must now activate the subscriber before checking for an IP.