Fix cluster formation BWC versions

We support JDK 10 through the 6.3 and 6.4 series. This commit adjusts
the BWC logic when starting nodes during tests to account for this.

buildSrc/src/main/groovy/org/elasticsearch/gradle/test/NodeInfo.groovy

@@ -177,11 +177,7 @@ class NodeInfo {
             javaVersion = 8
         } else if (nodeVersion.onOrAfter("6.2.0") && nodeVersion.before("6.3.0")) {
             javaVersion = 9
-        } else if (project.inFipsJvm && nodeVersion.onOrAfter("6.3.0") && nodeVersion.before("6.4.0")) {
-            /*
-             * Elasticsearch versions before 6.4.0 cannot be run in a FIPS-140 JVM. If we're running
-             * bwc tests in a FIPS-140 JVM, ensure that the pre v6.4.0 nodes use a Java 10 JVM instead.
-             */
+        } else if (nodeVersion.onOrAfter("6.3.0") && nodeVersion.before("6.5.0")) {
             javaVersion = 10
         }