Improve Windows setup script Android bits

Changes include:
	* In case `ANDROID_HOME` environment variable is not set, try to determine the correct path to `android-sdk` through `android.bat`'s location
	* Use `android.bat` executable relative to `android-sdk`, set in `ANDROID_HOME` environment variable, for sdk updates
	* Split android sdk updates into single command calls in order to avoid problems with license agreements

Author: Dimitar Kerezov

setup/native-script.ps1

@@ -71,16 +71,21 @@ Install "Google Chrome" "Installing Google Chrome (required to debug NativeScrip
 Install "Java Development Kit" "Installing Java Development Kit" "cinst jdk8 --force --yes"
 
 Install "Android SDK" "Installing Android SDK" "cinst android-sdk --force --yes"
-
-# setup android sdk
-echo yes | cmd /c "$env:localappdata\Android\android-sdk\tools\android" update sdk --filter "tools,platform-tools,android-23" --all --no-ui
-echo yes | cmd /c "$env:localappdata\Android\android-sdk\tools\android" update sdk --filter "build-tools-23.0.1,extra-android-m2repository" --all --no-ui
-
 # setup environment
 
 if (!$env:ANDROID_HOME) {
-	[Environment]::SetEnvironmentVariable("ANDROID_HOME", "$env:localappdata\Android\android-sdk", "User")
-	$env:ANDROID_HOME = "$env:localappdata\Android\android-sdk";
+	# in case the user has `android` in the PATH, use it as base for setting ANDROID_HOME
+	$androidExecutableEnvironmentPath = Get-Command android -ErrorAction SilentlyContinue | Select-Object -ExpandProperty Definition
+	if ($androidExecutableEnvironmentPath -ne $null) {
+		$androidHomeJoinedPath = [io.path]::combine($androidExecutableEnvironmentPath, "..", "..")
+		$androidHome = Resolve-Path $androidHomeJoinedPath | Select-Object -ExpandProperty Path
+	}
+	else {
+		$androidHome = "$env:localappdata\Android\android-sdk"
+	}
+
+	$env:ANDROID_HOME = $androidHome;
+	[Environment]::SetEnvironmentVariable("ANDROID_HOME", "$env:ANDROID_HOME", "User")
 }
 
 if (!$env:JAVA_HOME) {
@@ -90,5 +95,16 @@ if (!$env:JAVA_HOME) {
 	$env:JAVA_HOME = $javaHome;
 }
 
+# setup android sdk
+# following commands are separated in case of having to answer to license agreements
+# the android tool will introduce a --accept-license option in subsequent releases
+$androidExecutable = [io.path]::combine($env:ANDROID_HOME, "tools", "android")
+echo y | cmd /c "$androidExecutable" update sdk --filter "tools" --all --no-ui
+echo y | cmd /c "$androidExecutable" update sdk --filter "platform-tools" --all --no-ui
+echo y | cmd /c "$androidExecutable" update sdk --filter "android-23" --all --no-ui
+echo y | cmd /c "$androidExecutable" update sdk --filter "build-tools-23.0.2" --all --no-ui
+echo y | cmd /c "$androidExecutable" update sdk --filter "extra-android-m2repository" --all --no-ui
+
+
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