android: dont lookup to android sdk/ndk if we didnt change the buildozer.spec options related to it, and if everything was working in the first time.

buildozer/targets/android.py

@@ -354,6 +354,19 @@ class TargetAndroid(Target):
         return package_versions[-1]
 
     def _install_android_packages(self):
+
+        # if any of theses value change into the buildozer.spec, retry the
+        # update
+        cache_key = 'android:sdk_installation'
+        cache_value = [
+            self.android_api,
+            self.android_minapi,
+            self.android_ndk_version,
+            self.android_sdk_dir,
+            self.android_ndk_dir]
+        if self.buildozer.state.get(cache_key, None) == cache_value:
+            return True
+
         # 3 pass installation.
         if not os.access(self.android_cmd, os.X_OK):
             self.buildozer.cmd('chmod ug+x {}'.format(self.android_cmd))
@@ -382,6 +395,9 @@ class TargetAndroid(Target):
 
         self.buildozer.info('Android packages installation done.')
 
+        self.buildozer.state[cache_key] = cache_value
+        self.buildozer.state.sync()
+
     def install_platform(self):
         cmd = self.buildozer.cmd
         self.pa_dir = pa_dir = join(self.buildozer.platform_dir, 'python-for-android')