Take local.properties into account when checking for Android SDK

samples/calculator/android/build.gradle

@@ -8,7 +8,7 @@ buildscript {
 
     dependencies {
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
-        classpath 'com.android.tools.build:gradle:3.1.0'
+        classpath 'com.android.tools.build:gradle:3.1.3'
     }
 }
 

samples/calculator/settings.gradle

@@ -2,7 +2,14 @@ include ':common'
 include ':jvm'
 include ':ios'
 
-if (System.getenv('ANDROID_HOME') != null) {
+def localProperties = new Properties()
+def localPropertiesFile = file('local.properties')
+if (localPropertiesFile.exists()) {
+    localPropertiesFile.withReader { localProperties.load(it) }
+}
+
+// Don't create Android tasks if a user has no Android SDK.
+if (localProperties.containsKey("sdk.dir") || System.getenv('ANDROID_HOME') != null) {
     include ':android'
 }