Add support for booting with a boot classpath not fully AOTed.

Bug: 119800099
Test: adb shell setprop dalvik.vm.boot-image "/system/framework/nonexistent.art"

Change-Id: I6641399f43c24702f19f4d976c6054d77186799e
diff --git a/runtime/parsed_options.cc b/runtime/parsed_options.cc
index f516d0d..e644c04 100644
--- a/runtime/parsed_options.cc
+++ b/runtime/parsed_options.cc
@@ -609,8 +609,7 @@
   }
 
   if (!args.Exists(M::CompilerCallbacksPtr) && !args.Exists(M::Image)) {
-    std::string image = GetAndroidRoot();
-    image += "/framework/boot.art";
+    std::string image = GetDefaultBootImageLocation(GetAndroidRoot());
     args.Set(M::Image, image);
   }