Use Strict version check for VersionCompatibilityTests

This changes the loose usage of onOrBefore to equals so that when we add beta1, this test fails
again.

Original commit: elastic/x-pack-elasticsearch@fe4f2cbdf0

elasticsearch/x-pack/shield/src/test/java/org/elasticsearch/shield/VersionCompatibilityTests.java

@@ -37,6 +37,6 @@ public class VersionCompatibilityTests extends ESTestCase {
          *
          */
         assertThat("Remove workaround in LicenseService class when es core supports merging cluster level custom metadata",
-                Version.CURRENT.onOrBefore(Version.V_5_0_0_alpha2), is(true));
+                   Version.CURRENT.equals(Version.V_5_0_0), is(true));
     }
 }