Add backwards-compatibility ocamlfind subpackages

As part of the jbuilder converstion, the packages

  xenstore_transport
  xenstore_transport.unix
  xenstore_transport.lwt

were merged into `xenstore_transport`. This patch adds aliases to the
META file so we don't needlessly break the build of other components
which try to link with the subpackage.

This fixes the build of packages like vhd-tool, see
ocaml/opam-repository#9481 (comment)

Signed-off-by: David Scott <[email protected]>

Author: djs55

META.xenstore_transport.template

@@ -0,0 +1,11 @@
+# JBUILDER_GEN
+
+package "unix" (
+  description = "Deprecated. Use xenstore_transport"
+  requires = "xenstore_transport"
+)
+
+package "lwt" (
+  description = "Deprecated. Use xenstore_transport"
+  requires = "xenstore_transport"
+)