tests: shell: change all test scripts to return 0

tests: shell: change all test scripts to return 0

The shell-based tests currently encode a return value in the
file name, i.e. foo_1 expects that the script should return '1'
for the test case to pass.

This is very error prone, and one test case is even broken (i.e.,
it returns 1, but because of a different, earlier error).

do_something || exit 1
or
'set -e'

are both pretty common patterns, in both cases tests should fail.

In those test-cases that deliberately test for an error,
nft something_should_fail || exit 0
nft something_should_fail && exit 1

or a similar constructs should be used.

This initial commit modififies all '_1' scripts to return 0 on
success, usually via 'nft wrong || exit 0'.

All tests pass, except the one broken test case that hasn't worked
before either, but where 'set -e' use made it pass (the failing command
is supposed to work, and the command that is supposed to fail is never
run).

Signed-off-by: Florian Westphal <fw@strlen.de>