system tests: add assert(), and start using it

Problem: the system test 'is()' checker was poorly thought out.
For example, there is no way to check for inequality or for
absence of a substring.

Solution, step 1: introduce new assert(), copied almost verbatim
from buildah, where it has been successful in addressing the
gaps in is().

The logical next step is to search the tests for 'die' and
for 'run', looking for negative assertions which we can
replace with assert(). There were a lot, and in the process
I found a number of ugly bugs in the tests themselves. I've
taken the liberty of fixing these.

Important note: at this time we have both assert() and is().
Replacing all instances of is() would be impossible to review.

Signed-off-by: Ed Santiago <santiago@redhat.com>

0 files changed, 0 insertions, 0 deletions