Support testing Direct Reply with EditTextVariations on API 24/25

This is a follow up CL to my previous CL [1], which enabled us to test
Direct-Reply with EditTextVariations.

What this CL does are:

 * Specyfing min_sdk_version to avoid INSTALL_FAILED_OLDER_SDK error
   when installing on older devices.
 * Avoiding NoSuchMethodError on pre-O devices where
   Notification.Builder does not have a constructor that takes
   notification channel.
 * Fixing a race condition where notification can be sent before
   notification channel is created.

 [1]: Iafffcc7d138b0f502116a5e557f0c3f17e9d0b73
      da2486fd63d7d46e982d0e2fb2eba3dac07aff32

Bug: 122957841
Test: Made sure that we can install EditTextVariations on N devices
      and "Direct-Reply" on EditTextVariations works there.
Change-Id: Ib4fbd447608b111e763fde4287226cf7e206e65e
diff --git a/tools/EditTextVariations/Android.bp b/tools/EditTextVariations/Android.bp
index 36296a5..94b4951 100644
--- a/tools/EditTextVariations/Android.bp
+++ b/tools/EditTextVariations/Android.bp
@@ -18,4 +18,5 @@
     srcs: ["src/**/*.java"],
 
     sdk_version: "current",
+    min_sdk_version: "11",
 }