check: deprecate using process sessions to isolate test instances

check: deprecate using process sessions to isolate test instances

As I've noted elsewhere, the use of process session ids to "isolate"
test instances from killing each other is kind of hacky and creates
other weird side effects.  I'd rather everyone use the new code that
runs everything in proper isolation with private pid and mount
namespaces, but I don't know how many people this would break were it a
hard dependency.

Deprecate the process session handling immediately with a warning that
we're going to rip it out in a year.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>