VOL-1845 : Support for delete device in openolt adapter

           This commit is for the handling of delete device.

           The changes are done to handle the request for delete
           device. This includes the clearing of all data related
           to the device in KV store and reboot of device to reset
           the device.

           This commit has dependency in voltha-go so that needs to
           be merged first. Please refer this review link
           https://gerrit.opencord.org/#/c/15084/

           Updated to dep ensure above voltha-go patch set.  Also typo
           and make lint/sca fixes.

Change-Id: I53f16022c6902d498dad30e9b7d0ff50bf156347
diff --git a/vendor/go.etcd.io/etcd/clientv3/concurrency/mutex.go b/vendor/go.etcd.io/etcd/clientv3/concurrency/mutex.go
index 0135341..306470b 100644
--- a/vendor/go.etcd.io/etcd/clientv3/concurrency/mutex.go
+++ b/vendor/go.etcd.io/etcd/clientv3/concurrency/mutex.go
@@ -16,6 +16,7 @@
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"sync"
 
@@ -23,6 +24,9 @@
 	pb "go.etcd.io/etcd/etcdserver/etcdserverpb"
 )
 
+// ErrLocked is returned by TryLock when Mutex is already locked by another session.
+var ErrLocked = errors.New("mutex: Locked by another session")
+
 // Mutex implements the sync Locker interface with etcd
 type Mutex struct {
 	s *Session
@@ -37,9 +41,56 @@
 	return &Mutex{s, pfx + "/", "", -1, nil}
 }
 
+// TryLock locks the mutex if not already locked by another session.
+// If lock is held by another session, return immediately after attempting necessary cleanup
+// The ctx argument is used for the sending/receiving Txn RPC.
+func (m *Mutex) TryLock(ctx context.Context) error {
+	resp, err := m.tryAcquire(ctx)
+	if err != nil {
+		return err
+	}
+	// if no key on prefix / the minimum rev is key, already hold the lock
+	ownerKey := resp.Responses[1].GetResponseRange().Kvs
+	if len(ownerKey) == 0 || ownerKey[0].CreateRevision == m.myRev {
+		m.hdr = resp.Header
+		return nil
+	}
+	client := m.s.Client()
+	// Cannot lock, so delete the key
+	if _, err := client.Delete(ctx, m.myKey); err != nil {
+		return err
+	}
+	m.myKey = "\x00"
+	m.myRev = -1
+	return ErrLocked
+}
+
 // Lock locks the mutex with a cancelable context. If the context is canceled
 // while trying to acquire the lock, the mutex tries to clean its stale lock entry.
 func (m *Mutex) Lock(ctx context.Context) error {
+	resp, err := m.tryAcquire(ctx)
+	if err != nil {
+		return err
+	}
+	// if no key on prefix / the minimum rev is key, already hold the lock
+	ownerKey := resp.Responses[1].GetResponseRange().Kvs
+	if len(ownerKey) == 0 || ownerKey[0].CreateRevision == m.myRev {
+		m.hdr = resp.Header
+		return nil
+	}
+	client := m.s.Client()
+	// wait for deletion revisions prior to myKey
+	hdr, werr := waitDeletes(ctx, client, m.pfx, m.myRev-1)
+	// release lock key if wait failed
+	if werr != nil {
+		m.Unlock(client.Ctx())
+	} else {
+		m.hdr = hdr
+	}
+	return werr
+}
+
+func (m *Mutex) tryAcquire(ctx context.Context) (*v3.TxnResponse, error) {
 	s := m.s
 	client := m.s.Client()
 
@@ -53,28 +104,13 @@
 	getOwner := v3.OpGet(m.pfx, v3.WithFirstCreate()...)
 	resp, err := client.Txn(ctx).If(cmp).Then(put, getOwner).Else(get, getOwner).Commit()
 	if err != nil {
-		return err
+		return nil, err
 	}
 	m.myRev = resp.Header.Revision
 	if !resp.Succeeded {
 		m.myRev = resp.Responses[0].GetResponseRange().Kvs[0].CreateRevision
 	}
-	// if no key on prefix / the minimum rev is key, already hold the lock
-	ownerKey := resp.Responses[1].GetResponseRange().Kvs
-	if len(ownerKey) == 0 || ownerKey[0].CreateRevision == m.myRev {
-		m.hdr = resp.Header
-		return nil
-	}
-
-	// wait for deletion revisions prior to myKey
-	hdr, werr := waitDeletes(ctx, client, m.pfx, m.myRev-1)
-	// release lock key if wait failed
-	if werr != nil {
-		m.Unlock(client.Ctx())
-	} else {
-		m.hdr = hdr
-	}
-	return werr
+	return resp, nil
 }
 
 func (m *Mutex) Unlock(ctx context.Context) error {