save: wire up trivial save/restore flags implementations

save: wire up trivial save/restore flags implementations

For all hypervisors that support save and restore, the new API
now performs the same functions as the old.

VBox is excluded from this list, because its existing domainsave
is broken (there is no corresponding domainrestore, and there
is no control over the filename used in the save).  A later
patch should change vbox to use its implementation for
managedsave, and teach start to use managedsave results.

* src/libxl/libxl_driver.c (libxlDomainSave): Move guts...
(libxlDomainSaveFlags): ...to new function.
(libxlDomainRestore): Move guts...
(libxlDomainRestoreFlags): ...to new function.
* src/test/test_driver.c (testDomainSave, testDomainSaveFlags)
(testDomainRestore, testDomainRestoreFlags): Likewise.
* src/xen/xen_driver.c (xenUnifiedDomainSave)
(xenUnifiedDomainSaveFlags, xenUnifiedDomainRestore)
(xenUnifiedDomainRestoreFlags): Likewise.
* src/qemu/qemu_driver.c (qemudDomainSave, qemudDomainRestore):
Rename and move guts.
(qemuDomainSave, qemuDomainSaveFlags, qemuDomainRestore)
(qemuDomainRestoreFlags): ...here.
(qemudDomainSaveFlag): Rename...
(qemuDomainSaveInternal): ...to this, and update callers.