osrelease-detector: avoid colliding with other detectors

Due to the detector registration and fact that their in a non-ordered
map, it is random whether the osrelease or redhatrelease detector would
hit. And likely resulted in alternately formatted namespace strings.

This change causes the osrelease to not detect when data has
centos-release or redhat-release, which is not _great_ because if the
redhatrelease detector is not compiled in, then that would not be a
fallback that the osrelease detector could rely on. :-\

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

worker/detectors/namespace/osrelease/osrelease.go

@@ -24,6 +24,8 @@ import (
 )
 
 var (
+	//log = capnslog.NewPackageLogger("github.com/coreos/clair", "worker/detectors/namespace/osrelease")
+
 	osReleaseOSRegexp      = regexp.MustCompile(`^ID=(.*)`)
 	osReleaseVersionRegexp = regexp.MustCompile(`^VERSION_ID=(.*)`)
 )
@@ -42,6 +44,12 @@ func init() {
 func (detector *OsReleaseNamespaceDetector) Detect(data map[string][]byte) *database.Namespace {
 	var OS, version string
 
+	for _, filePath := range detector.getExcludeFiles() {
+		if _, hasFile := data[filePath]; hasFile {
+			return nil
+		}
+	}
+
 	for _, filePath := range detector.GetRequiredFiles() {
 		f, hasFile := data[filePath]
 		if !hasFile {
@@ -74,3 +82,8 @@ func (detector *OsReleaseNamespaceDetector) Detect(data map[string][]byte) *data
 func (detector *OsReleaseNamespaceDetector) GetRequiredFiles() []string {
 	return []string{"etc/os-release", "usr/lib/os-release"}
 }
+
+// getExcludeFiles returns the list of files that are ought to exclude this detector from Detect()
+func (detector *OsReleaseNamespaceDetector) getExcludeFiles() []string {
+	return []string{"etc/redhat-release", "usr/lib/centos-release"}
+}