Having these named differently than the test itself mostly creates
unecessary confusion and makes writing logic against the tests harder
so let's rename the testsuite-xx units and scripts to just use the
test name itself.
Let's make this behave more like all the rest of the meson stuff.
This also is the first step to making it a bit more flexible so we
can define integration tests in different ways as will be seen in
the next commits.
It never worked, but the fail was masked by missing set -e, see the
previous commit.
Also, throw env into the test container and dump the environment on
container start, to make potential failures easier to debug.
It already required a lot of workarounds, since the busybox utilities
often work differently than their "full" counterparts, and putting
the container together using our "tools" is quite simple anyway.
