On shell 'exit' commands, running shells from pasta, we might get:

  Cannot set tty process group (No such process)

as some TTY devices might be unaccessible. This is harmless, but
after commit "pasta: propagate exit code from child command", we'll
get test failures there, at least with dash.

Ignore those explicitly with a ugly workaround: we can't simply do
something like:

	exit || :

because the failure is reported by the shell itself once it exits,
regardless of the command evaluation.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

To test log files on a tmpfs mount, we need to unshare the mount
namespace, which means using a context for the passt pane is not
really practical at the moment, as we can't open a shell there, so
we would have to encapsulate all the commands under 'unshare -rUm',
plus the "inner" pasta command, running in turn a tcp_rr server.

It might be worth fixing this by e.g. detecting we are trying to
spawn an interactive shell and adding a special path in the context
setup with some form of stdin redirection -- I'm not sure it's doable
though.

For this reason, add a new layout, using a context only for the host
pane, while keeping the old command dispatch mechanism for the passt
pane.

We also need a new setup function that doesn't start pasta: we want
to start and restart it with different options.

Further, we need a 'pint' directive, to send an interrupt to the
passt pane: add that in lib/test.

All the tests before the one involving tmpfs and a detached mount
namespace were also tested with the context mechanism. To make an
eventual conversion easier, pass tcp_crr directly as a command on
pasta's command line where feasible.

While at it, fix the comment to the teardown_pasta() function.

The new test set can be semi-conveniently run as:

  ./run pasta_options/log_to_file

and it checks basic log creation, size of the log file after flooding
it with debug entries, rotations, and basic consistency after
rotations, on both an existing filesystem and a tmpfs, chosen as
it doesn't support collapsing data ranges via fallocate(), hence
triggering the fall-back mechanism for logging rotation.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>