Custom signing script for the Virt APEX

Custom signing script is a command line tool to sign the virt apex
contents. It re-signs filesystem images and bootloader with a given key.

This will be executed in apex_util.py as a part of release key signing
process.

Bug: 193504286
Test: deapexer extract com.android.virt.apex extracted
      sign_virt_apex -v key.pem extracted
Change-Id: Iee3730afd828b95268220c4c9a9ad7884eb3e54e
diff --git a/apex/Android.bp b/apex/Android.bp
index 17ff7da..20a863f 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -83,3 +83,20 @@
     filename: "init.rc",
     installable: false,
 }
+
+// Virt apex needs a custom signer for its payload
+python_binary_host {
+    name: "sign_virt_apex",
+    srcs: [
+        "sign_virt_apex.py",
+    ],
+    version: {
+        py2: {
+            enabled: false,
+        },
+        py3: {
+            enabled: true,
+            embedded_launcher: true,
+        },
+    },
+}