test: increase specificity in dgram test

Expand error message checking to include the entire error string in test-dgram-membership. PR-URL: nodejs#11187 Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com> Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com> Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: Trott

test/parallel/test-dgram-membership.js

@@ -14,7 +14,7 @@ const setup = () => {
  const socket = setup();
  socket.close(common.mustCall(() => {
  assert.throws(() => { socket.addMembership(multicastAddress); },
- /Not running/);
+ /^Error: Not running$/);
  }));
 }
 
@@ -23,23 +23,23 @@ const setup = () => {
  const socket = setup();
  socket.close(common.mustCall(() => {
  assert.throws(() => { socket.dropMembership(multicastAddress); },
- /Not running/);
+ /^Error: Not running$/);
  }));
 }
 
 // addMembership() with no argument should throw
 {
  const socket = setup();
  assert.throws(() => { socket.addMembership(); },
- /multicast address must be specified/);
+ /^Error: multicast address must be specified$/);
  socket.close();
 }
 
 // dropMembership() with no argument should throw
 {
  const socket = setup();
  assert.throws(() => { socket.dropMembership(); },
- /multicast address must be specified/);
+ /^Error: multicast address must be specified$/);
  socket.close();
 }
 
@@ -69,7 +69,7 @@ const setup = () => {
  const socket = setup();
  assert.throws(
  () => { socket.dropMembership(multicastAddress); },
- /EADDRNOTAVAIL/
+ /^Error: dropMembership EADDRNOTAVAIL$/
  );
  socket.close();
 }