Add initial bp2build converter support for apex_key modules.

Test: Added unit test.

Change-Id: I1ec2adfcef770ff91bcf35b89d9961f4d2b8a814
diff --git a/bp2build/Android.bp b/bp2build/Android.bp
index dded14b..6ab062e 100644
--- a/bp2build/Android.bp
+++ b/bp2build/Android.bp
@@ -29,6 +29,7 @@
     ],
     testSrcs: [
         "apex_conversion_test.go",
+        "apex_key_conversion_test.go",
         "build_conversion_test.go",
         "bzl_conversion_test.go",
         "cc_library_conversion_test.go",