When doing import-environment, we shouldn't fail if some assignment is invalid.
OTOH, if the invalid assignment is specified as a positional argument, we should
keep failing.
This would also fix https://bugzilla.redhat.com/show_bug.cgi?id=1754395, by
ignoring certain variables which are not important in that scenario. It seems
like the right thing to do in general.
Zbigniew Jędrzejewski-Szmek
a4ccce22d9