change android native build scripts to not execute tasks at configuration time

jme3-android-native/openalsoft.gradle

@@ -75,7 +75,7 @@ task copyJmeOpenALSoft(type: Copy, dependsOn:copyOpenALSoft) {
 
 jar.into("lib") { from openalsoftBuildDir + File.separator + 'libs' }
 
-task generateOpenAlSoftHeaders(dependsOn:copyJmeOpenALSoft) {
+task generateOpenAlSoftHeaders(dependsOn:copyJmeOpenALSoft) <<{
     String destDir = openalsoftBuildDir + File.separator + 'jni'
 
     String classes = ""

jme3-android-native/stb_image.gradle

@@ -53,7 +53,7 @@ task copyStbiJmeFiles(type: Copy, dependsOn:copyStbiFiles) {
 
 jar.into("lib") { from stbiBuildDir + File.separator + 'libs' }
 
-task generateStbiHeaders(dependsOn:copyStbiJmeFiles) {
+task generateStbiHeaders(dependsOn:copyStbiJmeFiles) <<{
     String destDir = stbiBuildDir + File.separator + 'jni'
     String classes = ""
             .concat("com.jme3.texture.plugins.AndroidNativeImageLoader, ")