{import,export}_raw_vdi use vhd-tool via vhd_tool_wrapper

This allows both functions to use O_DIRECT.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
(cherry picked from commit 7de0edee16116204619d6634fc22bd4d8af5b745)

Conflicts:
	ocaml/xapi/OMakefile
	ocaml/xapi/import_raw_vdi.ml

Resolve Conflicts when merge to clearwater-sp1-lcm from creedence:
	ocaml/xapi/export_raw_vdi.ml
	ocaml/xapi/import_raw_vdi.ml
	ocaml/xapi/vhd_tool_wrapper.ml

Signed-off-by: Zheng Chai <zheng.chai@citrix.com>
Use Uuid instead of Uuidm

Signed-off-by: John Else <john.else@citrix.com>
Remove Re_str

Signed-off-by: John Else <john.else@citrix.com>
Fix xenstore

Signed-off-by: John Else <john.else@citrix.com>
Use Debug.Debugger instead of Debug.Make