create dockerImage stuff

bwa.wdl

@@ -13,7 +13,9 @@ task Mem {
         Int threads = 2
         Int memory = 8
         Int picardMemory = 4
-        String dockerTag = "43ec6124f9f4f875515f9548733b8b4e5fed9aa6-0"
+        # A mulled container is needed to have both picard and bwa in one container.
+        # This container contains: picard (2.18.7), bwa (0.7.17-r1188)
+        String dockerImage = "quay.io/biocontainers/mulled-v2-002f51ea92721407ef440b921fb5940f424be842:43ec6124f9f4f875515f9548733b8b4e5fed9aa6-0"
     }
 
     command {
@@ -40,10 +42,7 @@ task Mem {
     runtime{
         cpu: threads
         memory: memory + picardMemory + picardMemory
-        # A mulled container is needed to have both picard and bwa in one container.
-        # This container contains: picard (2.18.7), bwa (0.7.17-r1188)
-        docker: "quay.io/biocontainers/mulled-v2-002f51ea92721407ef440b921fb5940f424be842:" +
-            dockerTag
+        docker: dockerImage
     }
 }