tools/libxl: rename libxl__domain_suspend to libxl__domain_save

tools/libxl: rename libxl__domain_suspend to libxl__domain_save

The suspend/save terminology used by libxc is more consistent.
"suspend" refers to quiescing the VM, so pausing qemu, making a
remote_shutdown(SHUTDOWN_suspend) hypercall etc.
"save" refers to the actions involved in actually shuffling the
state of the VM, so xc_domain_save() etc.

libxl currently uses "suspend" to encapsulate both. The patch
Rename libxl__domain_suspend() to libxl__domain_save() since it
actually refers to shuffling the state of the VM.

This results in some strangeness in that some functions called *save*
are now passed a struct called *suspend*, this is temporary and is all
fixed up later by the refactoring of the suspend_state.

Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
Some comments, commit messages:
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <Ian.Campbell@citrix.com>