[VOL-1866] Changed module dependency to v12.0.0 of k8s client-go and v1.15.4 of k8s api/apimachinery in sync with other voltha components

Had to use pseudo-version corresponding to v12.0.0 of k8s client-go
because golang proxy is no longer serving the modules not complying
to Semantic Import Versioning rules including client-go v12.0.0.
Refer to https://github.com/kubernetes/client-go/issues/631 and
https://github.com/golang/go/issues/33558

Change-Id: I2e558bab7f0702f230761319eb5392a7d0532ea3
diff --git a/vendor/k8s.io/klog/klog_file.go b/vendor/k8s.io/klog/klog_file.go
index b76a4e1..e4010ad 100644
--- a/vendor/k8s.io/klog/klog_file.go
+++ b/vendor/k8s.io/klog/klog_file.go
@@ -97,9 +97,11 @@
 // contains tag ("INFO", "FATAL", etc.) and t.  If the file is created
 // successfully, create also attempts to update the symlink for that tag, ignoring
 // errors.
-func create(tag string, t time.Time) (f *os.File, filename string, err error) {
+// The startup argument indicates whether this is the initial startup of klog.
+// If startup is true, existing files are opened for appending instead of truncated.
+func create(tag string, t time.Time, startup bool) (f *os.File, filename string, err error) {
 	if logging.logFile != "" {
-		f, err := os.Create(logging.logFile)
+		f, err := openOrCreate(logging.logFile, startup)
 		if err == nil {
 			return f, logging.logFile, nil
 		}
@@ -113,7 +115,7 @@
 	var lastErr error
 	for _, dir := range logDirs {
 		fname := filepath.Join(dir, name)
-		f, err := os.Create(fname)
+		f, err := openOrCreate(fname, startup)
 		if err == nil {
 			symlink := filepath.Join(dir, link)
 			os.Remove(symlink)        // ignore err
@@ -124,3 +126,14 @@
 	}
 	return nil, "", fmt.Errorf("log: cannot create log: %v", lastErr)
 }
+
+// The startup argument indicates whether this is the initial startup of klog.
+// If startup is true, existing files are opened for appending instead of truncated.
+func openOrCreate(name string, startup bool) (*os.File, error) {
+	if startup {
+		f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
+		return f, err
+	}
+	f, err := os.Create(name)
+	return f, err
+}