NSHM Unit tests

When running NSHM unit tests in pipeline, instead of running the hazard calculation in the junit test itself the hazard calculation is done by running a java class and writing out the results to JSON files.

gradle/nshm.gradle

@@ -141,7 +141,7 @@ task testConus2018(type: Test) {
 
   useJUnitPlatform()
   jvmArgs(
-      "-Xms2g",
+      "-Xms${xmx}",
       "-Xmx${xmx}",
       )