REGTESTS: Explicitly allow failing shell commands in some scripts

Vtest2, that should replaced Vtest in few months, will reject any failing
commands in shell blocks. However, some scripts are executing some commands,
expecting an error to be able to parse the error output. So, now use "set
+e" in those scripts to explicitly state failing commads are expected.

It is just used for non-final commands. At the end, the shell block must
still report a success.

reg-tests/lua/close_wait_lf.vtc

@@ -49,6 +49,7 @@ client c1 -connect ${h1_frt_sock} -repeat 100  {
 syslog Slog -wait
 
 shell {
+    set +e
     ss -pt | grep CLOSE-WAIT.*haproxy.*pid=${h1_pid}
     exit $((!$?))
 }