in auto mode, generate both edify and amend scripts for full OTAs

Generate packages that can be installed by either amend or edify, so
we can remove amend support from donut.
diff --git a/tools/releasetools/ota_from_target_files b/tools/releasetools/ota_from_target_files
index ea4c752..4b7ee03 100755
--- a/tools/releasetools/ota_from_target_files
+++ b/tools/releasetools/ota_from_target_files
@@ -69,6 +69,7 @@
 import common
 import amend_generator
 import edify_generator
+import both_generator
 
 OPTIONS = common.OPTIONS
 OPTIONS.package_key = "build/target/product/security/testkey"
@@ -294,13 +295,15 @@
 
 
 def WriteFullOTAPackage(input_zip, output_zip):
-  if OPTIONS.script_mode in ("amend", "auto"):
+  if OPTIONS.script_mode == "auto":
+    script = both_generator.BothGenerator(2)
+  elif OPTIONS.script_mode == "amend":
     script = amend_generator.AmendGenerator()
   else:
     # TODO: how to determine this?  We don't know what version it will
     # be installed on top of.  For now, we expect the API just won't
     # change very often.
-    script = edify_generator.EdifyGenerator(1)
+    script = edify_generator.EdifyGenerator(2)
 
   if not OPTIONS.omit_prereq:
     ts = GetBuildProp("ro.build.date.utc", input_zip)