android: Use full path for gst android root path

This is needed in case we want to use any of the files from the unpacked
GStreamer for Android package in LOCAL_SRC_FILES (such as for prebuilt
libraries).

Author: ford-prefect

README.md

@@ -10,7 +10,7 @@ https://coaxion.net/blog/2014/10/gstreamer-remote-controlled-testing-application
 
 * Open the android-launch/ directory in Android Studio
   * If you downloaded the GStreamer for Android binary, set
-    `gstAndroidRoot = /path/to/gst-android-binaries` in `~/.gradle/gradle.properties`
+    `gstAndroidRoot = /path/to/gst-android-binaries` in `~/.gradle/gradle.properties` -- this must be an absolute path
   * If you built GStreamer for Android using Cerbero, you're good to go
-* Set up the NDK in Android Studio (under Project Structure, or set ANDROID_NDK_HOME in the environment, or ndk.dir in `local.properties`
+* Set up the NDK in Android Studio (under Project Structure, or set `ANDROID_NDK_HOME` in the environment, or ndk.dir in `local.properties`
 * Build the project in Android Studio like any other project

android-launch/app/build.gradle

@@ -7,7 +7,7 @@ def getNdkCommandLine(ndkRoot, target) {
     if (project.hasProperty('gstAndroidRoot'))
         gstRoot = project.gstAndroidRoot
     else
-        gstRoot = '~/cerbero/dist/android_arm'
+        gstRoot = System.properties['user.home'] + '/cerbero/dist/android_arm'
 
     if (ndkRoot == null)
         throw new GradleException('NDK not configured')