driver(container): fix conditional statement for error handling

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>
(cherry picked from commit 57d737a13c)

tests/rm.go

@@ -0,0 +1,12 @@
+package tests
+
+import (
+	"github.com/moby/buildkit/util/testutil/integration"
+)
+
+func rmCmd(sb integration.Sandbox, opts ...cmdOpt) (string, error) {
+	opts = append([]cmdOpt{withArgs("rm")}, opts...)
+	cmd := buildxCmd(sb, opts...)
+	out, err := cmd.CombinedOutput()
+	return string(out), err
+}