Changes

testenv: fix missing hasattr check

Fix that commands without a --distro argument ("./testenv.py init osmo-dev"
and "./testenv.py clean") fail with:

  AttributeError: 'Namespace' object has no attribute 'distro'

Fixes: 8d21add6 ("testenv: check for --distro without --podman")
Change-Id: I138fda5f5807588428bba4eb1593b887fe7357c9