set UTF-8 for android update command explicitly

Fix for fail in to update android package. It is happened to meet under the following conditions both.

* User environment is not used UTF-8 in default file.encoding in java
* Android-sdk license text is included not-ASCII code characters.

If user define JAVA_TOOL_OPTIONS in env, inherit it.

buildozer/targets/android.py

@@ -301,10 +301,12 @@ class TargetAndroid(Target):
 
     def _android_update_sdk(self, packages):
         from buildozer.libs.pexpect import EOF
+        java_tool_options = environ.get('JAVA_TOOL_OPTIONS', '')
         child = self.buildozer.cmd_expect('{} update sdk -u -a -t {}'.format(
             self.android_cmd, packages,
             cwd=self.buildozer.global_platform_dir),
-            timeout=None)
+            timeout=None,
+            env={'JAVA_TOOL_OPTIONS': java_tool_options + ' -Dfile.encoding=UTF-8'})
         while True:
             index = child.expect([EOF, '[y/n]: '])
             if index == 0: