Fix JDK-version dependent exception message parsing

This commit fixes some JDK-version dependent exception message checking
in the discovery node role tests.

Author: jasontedor

server/src/test/java/org/elasticsearch/cluster/node/DiscoveryNodeRoleTests.java

@@ -49,7 +49,7 @@ protected Setting<Boolean> roleSetting() {
                             }
 
                         })));
-        assertThat(e, hasToString(containsString("Duplicate key foo ")));
+        assertThat(e, hasToString(containsString("Duplicate key")));
     }
 
     public void testDiscoveryNodeSetPossibleRolesRejectsDuplicateRoleNameAbbreviations() {
@@ -72,7 +72,7 @@ protected Setting<Boolean> roleSetting() {
                             }
 
                         })));
-        assertThat(e, hasToString(containsString("Duplicate key f ")));
+        assertThat(e, hasToString(containsString("Duplicate key")));
     }
 
 }