Add vm_shell script

It's a small script that makes it easier to connect to a Microdroid VM
running in the Android device.

Usage: vm_shell [cid]

If cid is omitted it displays the CIDs of available VMs and lets you
select one.

Bug: N/A
Test: m vm_shell and run it
Change-Id: I762f1161024d151a2f9e75fdb217037f1f9a1e1d
diff --git a/vm/Android.bp b/vm/Android.bp
index f9eac4d..2e914c4 100644
--- a/vm/Android.bp
+++ b/vm/Android.bp
@@ -28,3 +28,8 @@
         "com.android.virt",
     ],
 }
+
+sh_binary_host {
+    name: "vm_shell",
+    src: "vm_shell.sh",
+}