Add utils for Archlinux

Signed-off-by: Nicolas Lamirault <nicolas.lamirault@gmail.com>

worker/detectors/packages/rpm_test.go

@@ -15,7 +15,6 @@
 package packages
 
 import (
-	"os/exec"
 	"testing"
 
 	"github.com/coreos/clair/database"
@@ -43,8 +42,7 @@ var rpmPackagesTests = []packagesTest{
 }
 
 func TestRpmPackagesDetector(t *testing.T) {
-	_, err := exec.LookPath("rpm")
-	if err != nil {
+	if checkPackageManager("rpm") != nil {
 		log.Warningf("could not find rpm executable. skipping")
 		return
 	}

worker/detectors/packages/test.go

@@ -16,6 +16,7 @@ package packages
 
 import (
 	"io/ioutil"
+	"os/exec"
 	"path"
 	"runtime"
 	"testing"
@@ -36,6 +37,11 @@ func loadFileForTest(name string) []byte {
 	return d
 }
 
+func checkPackageManager(name string) error {
+	_, err := exec.LookPath(name)
+	return err
+}
+
 func testPackagesDetector(t *testing.T, detector detectors.PackagesDetector, tests []packagesTest) {
 	for _, test := range tests {
 		packages, err := detector.Detect(test.data)