Add mbr-format, xe-unikernel-upload

Signed-off-by: David Scott <dave.scott@citrix.com>
mbr-format: add all the depopts of mirage-types(.lwt)

I need the mirage-types.lwt package, so I need to satisfy the full set
of depopts.

Signed-off-by: David Scott <dave.scott@citrix.com>
mbr-format: depend on cmdliner

Signed-off-by: David Scott <dave.scott@citrix.com>
mbr-format: depend on ocaml >= 4.00.0

Signed-off-by: David Scott <dave.scott@citrix.com>
Merge pull request #2471 from djs55/xe-unikernel-upload

Add mbr-format, xe-unikernel-upload