add "primaries" as a synonym for "masters" in named.conf

as "type primary" is preferred over "type master" now, it makes
sense to make "primaries" available as a synonym too.

added a correctness check to ensure "primaries" and "masters"
cannot both be used in the same zone.

(cherry picked from commit 16e14353b1)

bin/tests/system/dnssec/ns3/named.conf.in

@@ -42,7 +42,7 @@ zone "." {
 
 zone "example" {
 	type slave;
-	masters { 10.53.0.2; };
+	primaries { 10.53.0.2; };
 	file "example.bk";
 };
 
@@ -174,7 +174,7 @@ zone "multiple.example" {
 
 zone "rfc2335.example" {
 	type slave;
-	masters { 10.53.0.2; };
+	primaries { 10.53.0.2; };
 	file "rfc2335.example.bk";
 };
 
@@ -247,7 +247,7 @@ zone "split-smart.example" {
 zone "nsec3chain-test" {
 	type slave;
 	file "nsec3chain-test.bk";
-	masters { 10.53.0.2; };
+	primaries { 10.53.0.2; };
 };
 
 zone "expiring.example" {

bin/tests/system/dnssec/ns4/named4.conf.in

@@ -65,11 +65,11 @@ view auth {
 
 	zone secure.example {
 		type slave;
-		masters { 10.53.0.3; };
+		primaries { 10.53.0.3; };
 	};
 
 	zone insecure.secure.example {
 		type slave;
-		masters { 10.53.0.2; };
+		primaries { 10.53.0.2; };
 	};
 };

bin/tests/system/dnssec/ns7/named.conf.in

@@ -32,31 +32,31 @@ zone "." {
 
 zone "nsec3.example" {
 	type slave;
-	masters { 10.53.0.3; };
+	primaries { 10.53.0.3; };
 	file "nsec3.example.bk";
 };
 
 zone "optout.example" {
 	type slave;
-	masters { 10.53.0.3; };
+	primaries { 10.53.0.3; };
 	file "optout.example.bk";
 };
 
 zone "nsec3-unknown.example" {
 	type slave;
-	masters { 10.53.0.3; };
+	primaries { 10.53.0.3; };
 	file "nsec3-unknown.example.bk";
 };
 
 zone "optout-unknown.example" {
 	type slave;
-	masters { 10.53.0.3; };
+	primaries { 10.53.0.3; };
 	file "optout-unknown.example.bk";
 };
 
 zone "multiple.example" {
 	type slave;
-	masters { 10.53.0.3; };
+	primaries { 10.53.0.3; };
 	file "multiple.example.bk";
 };