Enable libsnapshot_cow in recovery builds

update_engine is enabled in recovery mode, needs to link with
libsnapshot_cow

Test: mm -j
Change-Id: Ia4823c866b16f47cd03dda1779701e957a77aed6
diff --git a/fs_mgr/libsnapshot/Android.bp b/fs_mgr/libsnapshot/Android.bp
index 77d21b2..04d7e27 100644
--- a/fs_mgr/libsnapshot/Android.bp
+++ b/fs_mgr/libsnapshot/Android.bp
@@ -145,6 +145,7 @@
         "libsnapshot_cow_defaults",
     ],
     host_supported: true,
+    recovery_available: true,
     shared_libs: [
         "libbase",
         "libcrypto",