Add convert_storage_key_to_ephemeral to keystore2_key access vector

Introduce the convert_storage_key_to_ephemeral permission to the
keystore2_key access vector and give vold permission to use it. This
permission must be checked when a caller wants to get a per-boot
ephemeral key from a long lived wrapped storage key.

Bug: 181806377
Bug: 181910578
Change-Id: I542c084a8fab5153bc98212af64234e62e9ad032
diff --git a/private/access_vectors b/private/access_vectors
index c1c0359..fdac890 100644
--- a/private/access_vectors
+++ b/private/access_vectors
@@ -731,6 +731,7 @@
 
 class keystore2_key
 {
+	convert_storage_key_to_ephemeral
 	delete
 	gen_unique_id
 	get_info