Changes

testenv: add TESTENV_REBUILD_OUTDATED_IMAGE

Add an environment variable that allows rebuilding the podman image
whenever it appears to be outdated. This is useful when working on the
Dockerfile. As requested by Pau.

Change-Id: Ia1243320b6d310c69ef9291cca69a1594b1a8a70

testenv: fix duplicate 2>&1

The pipe variable already has 2>&1, therefore we don't need to add it in
cmd.

Change-Id: Ifeae4c53b57f90242041e61ca5ab7073d155d7a8

mme: expect authentication during 2g->4G TAU procedure

If TAU happens without an existing security context, network for sure wants
to authenticate the UE. This is the scenario being tested here.

If there was a security context (eg. from a previous 4G Attach), then
it's up to the network to decide (or be capable) to implicitly
authenticate the UE.

Change-Id: I5ebcaf23a643b6cb97534328737257d26d3981fe