tests/int: don't add --root if $ROOT is not set

Some tests (those in help.bats and version.bats) do not use setup_bundle
(as they do not need to start any containers), and thus they do not set
$ROOT. As a consequence, these tests now call "runc --root /state" which
is not nice.

Make adding --root conditional (only if $ROOT is set).

Amazingly, this change breaks help.bats tests under rootless, because
"sudo rootless" does not change the value of XDG_RUNTIME_DIR which still
points to root-owned directory, and as a result we have this:

> runc foo -h (status=1):
> the path in $XDG_RUNTIME_DIR must be writable by the user
> time="2022-02-08T07:04:57Z" level=error msg="mkdir /run/user/0/runc: permission denied"

This could be fixed by adding proper $ROOT, but it's easier just to skip
those tests under non-root.

NOTE that version.bats is not broken because -v is handled by urfave/cli
very early, so app.Before function is not run.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

tests/integration/help.bats

@@ -2,6 +2,13 @@
 
 load helpers
 
+function setup() {
+	# It does not make sense to repeat these trivial tests for non-root.
+	# Also, they fail due to $ROOT not being set and XDG_RUNTIME_DIR
+	# pointing to another user's directory after sudo rootless.
+	requires root
+}
+
 @test "runc -h" {
 	runc -h
 	[ "$status" -eq 0 ]

tests/integration/helpers.bash

@@ -54,7 +54,8 @@ function runc() {
 
 # Raw wrapper for runc.
 function __runc() {
-	"$RUNC" ${RUNC_USE_SYSTEMD+--systemd-cgroup} --root "$ROOT/state" "$@"
+	"$RUNC" ${RUNC_USE_SYSTEMD+--systemd-cgroup} \
+		${ROOT:+--root "$ROOT/state"} "$@"
 }
 
 # Wrapper for runc spec.