Set scratch default to false when using Fusion

Signed-off-by: Ben Sherman <bentshermann@gmail.com>

modules/nextflow/src/main/groovy/nextflow/fusion/FusionScriptLauncher.groovy

@@ -62,7 +62,7 @@ class FusionScriptLauncher extends BashWrapperBuilder {
         bean.headerScript = headerScript(bean)
         // enable use of local scratch dir
         if( bean.scratch==null )
-            bean.scratch = true
+            bean.scratch = false
 
         return new FusionScriptLauncher(bean, scheme, remoteWorkDir)
     }