allow input of build number

build.gradle

@@ -47,12 +47,16 @@ ext {
     date = git.head().getDate().format("yy.MM.dd")
     revision = "-${git.head().abbreviatedId}"
     parents = git.head().parentIds;
+    if (project.hasProperty('buildnumber')) {
+        buildNumber = "$buildnumber"
+    } else {
         index = -2109;  // Offset to match CI
         for (; parents != null && !parents.isEmpty(); index++) {
             parents = git.getResolve().toCommit(parents.get(0)).getParentIds()
         }
         buildNumber = "${index}"
     }
+}
 
 if ( project.hasProperty("lzNoVersion") ) { // gradle build -PlzNoVersion
     version = "unknown"