Simplify tokenAwareHostPolicy.Pick

Main goal is to make `tokenAwareHostPolicy.Pick` code less convoluted.
But there are little functional changes:
Before this PR hosts from tablets are not being shuffled
There are three host information sources: tablets, meta and tokenring,
Before this PR if tables returned no hosts for given token, in certain cases code did not consider meta or tokenring.
And same for meta, it did not consider tokenring.
After this PR, it starts goes through tablets, meta and tokenring, if current host sources yield no hosts it proceed to next one.

policies.go

@@ -651,15 +651,12 @@ func (t *tokenAwareHostPolicy) Pick(qry ExecutableQuery) NextHost {
 	var replicas []*HostInfo
 
 	if qry.GetSession() != nil && qry.GetSession().tabletsRoutingV1 {
-		t.tablets.mu.Lock()
 		tablets := t.tablets.get()
 
 		// Search for tablets with Keyspace and Table from the Query
 		l, r := findTablets(tablets, qry.Keyspace(), qry.Table())
 		if l != -1 {
 			tablet := findTabletForToken(tablets, token, l, r)
-
-			replicas = []*HostInfo{}
 			hosts := t.hosts.get()
 			for _, replica := range tablet.Replicas() {
 				for _, host := range hosts {
@@ -669,36 +666,25 @@ func (t *tokenAwareHostPolicy) Pick(qry ExecutableQuery) NextHost {
 					}
 				}
 			}
-		} else {
-			ht := meta.replicas[qry.Keyspace()].replicasFor(token)
-
-			if ht == nil {
-				host, _ := meta.tokenRing.GetHostForToken(token)
-				replicas = []*HostInfo{host}
-			} else {
-				replicas = ht.hosts
-			}
-		}
-
-		if t.shuffleReplicas && !qry.IsLWT() {
-			replicas = shuffleHosts(replicas)
 		}
+	}
 
-		t.tablets.mu.Unlock()
-	} else {
+	if len(replicas) == 0 {
 		ht := meta.replicas[qry.Keyspace()].replicasFor(token)
-
-		if ht == nil {
-			host, _ := meta.tokenRing.GetHostForToken(token)
-			replicas = []*HostInfo{host}
-		} else {
+		if ht != nil {
 			replicas = ht.hosts
-			if t.shuffleReplicas && !qry.IsLWT() {
-				replicas = shuffleHosts(replicas)
-			}
 		}
 	}
 
+	if len(replicas) == 0 {
+		host, _ := meta.tokenRing.GetHostForToken(token)
+		replicas = []*HostInfo{host}
+	}
+
+	if t.shuffleReplicas && !qry.IsLWT() && len(replicas) > 1 {
+		replicas = shuffleHosts(replicas)
+	}
+
 	if s := qry.GetSession(); s != nil && t.avoidSlowReplicas {
 		healthyReplicas := make([]*HostInfo, 0, len(replicas))
 		unhealthyReplicas := make([]*HostInfo, 0, len(replicas))