revert changes to fromPkcs8

Author: mpeddada1

oauth2_http/java/com/google/auth/oauth2/ServiceAccountJwtAccessCredentials.java

@@ -234,7 +234,7 @@ public static ServiceAccountJwtAccessCredentials fromPkcs8(
         privateKeyId,
         defaultAudience,
         null,
-        null);
+            Credentials.GOOGLE_DEFAULT_UNIVERSE);
   }
 
   static ServiceAccountJwtAccessCredentials fromPkcs8(

oauth2_http/javatests/com/google/auth/oauth2/ServiceAccountJwtAccessCredentialsTest.java

@@ -884,7 +884,7 @@ public void fromPkcs8_NoUniverseDomain() throws IOException {
     assertEquals(
         OAuth2Utils.privateKeyFromPkcs8(SA_PRIVATE_KEY_PKCS8), credentials.getPrivateKey());
     assertNull(credentials.getQuotaProjectId());
-    assertNull(credentials.getUniverseDomain());
+    assertEquals(Credentials.GOOGLE_DEFAULT_UNIVERSE, credentials.getUniverseDomain());
   }
 
   @Test