[Android] Allow project to specify Axmol engine root path (#2361)

* Use System.properties.AX_ROOT to store engine path
Allow Android builds to specify Axmol engine path

* If axmol folder exists in the root of the project folder, then use that for the engine path

core/platform/android/libaxmol/axutils.gradle

@@ -178,11 +178,19 @@ class AxmolUtils {
         return buildProfiles
     }
 
+    private static getEngineRoot() {
+        def axRoot = System.getProperty("AX_ROOT");
+        if (axRoot == null) {
+            axRoot = System.getenv("AX_ROOT");
+        }
+        return axRoot;
+    }
+
     private static Properties loadProfiles(project, isAxmolAppProj) {
         // build.profiles in axmol engine
         def profiles = new Properties()
         try {
-            profiles.load(new File(Paths.get("${System.env.AX_ROOT}/1k/build.profiles").toUri()).newDataInputStream())
+            profiles.load(new File(Paths.get("${getEngineRoot()}/1k/build.profiles").toUri()).newDataInputStream())
         }
         catch(ignored) {
         }
@@ -311,7 +319,7 @@ class AxmolUtils {
             cmakeBinDirs.add(cmakeBinDir)
         }
 
-        cmakeBinDir = joinPath(Paths.get("${System.env.AX_ROOT}").toAbsolutePath().toString(), 'tools', 'external', 'cmake', 'bin')
+        cmakeBinDir = joinPath(Paths.get("${getEngineRoot()}").toAbsolutePath().toString(), 'tools', 'external', 'cmake', 'bin')
         cmakeBinDirs.add(cmakeBinDir)
 
         // find in cmakeBinDirs
@@ -327,7 +335,7 @@ class AxmolUtils {
 
         if (index == (cmakeBinDirs.size() - 1)) {
             // using  cmakeBinDir=axmol/tools/external/cmake/bin
-            buildProfiles['cmakeDir'] = joinPath(Paths.get("${System.env.AX_ROOT}").toAbsolutePath().toString(), 'tools', 'external', 'cmake')
+            buildProfiles['cmakeDir'] = joinPath(Paths.get("${getEngineRoot()}").toAbsolutePath().toString(), 'tools', 'external', 'cmake')
         }
 
         if(foundCMakeVer == null) {

templates/common/proj.android/settings.gradle

@@ -1,6 +1,14 @@
 import java.nio.file.Paths
+
+def folder = new File("${settingsDir}/../axmol")
+if (folder.exists()) {
+    System.setProperty("AX_ROOT", folder.path)
+} else {
+    System.setProperty("AX_ROOT", "${System.env.AX_ROOT}")
+}
+
 include ':libaxmol'
-project(':libaxmol').projectDir = new File(Paths.get("${System.env.AX_ROOT}/core/platform/android/libaxmol").toUri())
+project(':libaxmol').projectDir = new File(Paths.get("${System.properties.AX_ROOT}/core/platform/android/libaxmol").toUri())
 include ':Dummy'
 project(':Dummy').projectDir = new File(settingsDir, 'app')
 rootProject.name = "Dummy"