containers#1533

Some changes by Debarshi Ray.

containers#957
containers#1052

The test suite uses its own separate local container/storage store to
isolate itself from the default store, so that the tests' interactions
with containers and images don't affect anything else.  This is done by
using the CONTAINERS_STORAGE_CONF environment variable [1] to specify a
separate storage.conf(5) file [2].

Therefore, when running the test suite, the CONTAINERS_STORAGE_CONF
environment variable must be preserved when forwarding toolbox(1)
invocations inside containers to the host.  Otherwise, the initial
toolbox(1) invocation on the host and the forwarded invocation running
on the host won't use the same local container/storage store.

This problem only impacts test cases that cover toolbox(1) code paths
that invoke podman(1).

[1] https://docs.podman.io/en/latest/markdown/podman.1.html

[2] https://manpages.debian.org/testing/containers-storage/containers-storage.conf.5.en.html

containers#957
containers#1052

The lines were getting too wide to fit within a vertical 1080x1920
display.  Therefore, restrict them to 120 characters per line.

Fallout from f8e21a3

containers#1534

When 'toolbox run' is invoked on the host, an exit code of 126 from
'podman exec' means that the specified command couldn't be invoked
because it's not an executable.  eg., the command was actually a
directory.  Note that this doesn't mean that the command couldn't be
found.  That's denoted by exit code 127.

Secondly, Toolbx containers always have an executable toolbox(1) binary
at /usr/bin/toolbox and it's assumed that /usr/bin is always part of the
PATH environment variable.

When 'toolbox run toolbox ...' is invoked, the inner toolbox(1)
invocation will be forwarded back to the host by the Toolbx container's
/usr/bin/toolbox, which is always present as an executable.  Hence, if
the outer 'podman exec' on the host fails with an exit code of 126,
then it doesn't mean that the container didn't have a working toolbox(1)
executable, but that some subordinate process started by the container's
toolbox(1) failed with that exit code.

Therefore, handle this as a special case to avoid showing an extra error
message.  Otherwise, it leads to:
  $ toolbox run toolbox run /etc
  bash: line 1: /etc: Is a directory
  bash: line 1: exec: /etc: cannot execute: Is a directory
  Error: failed to invoke command /etc in container fedora-toolbox-40
  Error: failed to invoke command toolbox in container fedora-toolbox-40
  $ echo "$?"
  126

Instead, it will now be:
  $ toolbox run toolbox run /etc
  bash: line 1: /etc: Is a directory
  bash: line 1: exec: /etc: cannot execute: Is a directory
  Error: failed to invoke command /etc in container fedora-toolbox-40
  $ echo "$?"
  126

containers#957
containers#1052