android: add ability to make test signed release builds

android/app/build.gradle

         }
     }
 
+    signingConfigs {
+        debug {
+            storeFile file('debug.keystore')
+            storePassword 'android'
+            keyAlias 'androiddebugkey'
+            keyPassword 'android'
+        }
+    }
+
     buildTypes {
         debug {
             buildConfigField "boolean", "GOOGLE_SERVICES_ENABLED", "${googleServicesEnabled}"
             buildConfigField "boolean", "LIBRE_BUILD", "${rootProject.ext.libreBuild}"
         }
         release {
+            // Uncomment the following line for singing a test release build.
+            //signingConfig signingConfigs.debug
             minifyEnabled true
             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules-release.pro'
             buildConfigField "boolean", "GOOGLE_SERVICES_ENABLED", "${googleServicesEnabled}"