GEODE-1213: Enable signing archives on geode-assembly

The disableMavenPublishing task was used on both geode-modules-assembly
and geode-assembly. But geode-assembly does have archives that need to
be signed, so we should not disable signing for this module.

Adding a separate disableSigning method to disable signing, which is
used only in the geode-modules-assembly.

extensions/geode-modules-assembly/build.gradle

@@ -38,6 +38,7 @@ extraArchive {
 }
 
 disableMavenPublishing()
+disableSigning()
 
 def getJarArtifact(module) {
   project(module).configurations.archives.artifacts.findAll {

gradle/utilities.gradle

@@ -33,6 +33,11 @@ allprojects {
       afterEvaluate {
         install.enabled = false
         uploadArchives.enabled = false
+      }
+    }
+    disableSigning = {
+      // Use this closure when a project should not publish anything to maven.
+      afterEvaluate {
         signArchives.enabled = false
       }
     }