libxl: further fixups re LIBXL_DOMAIN_TYPE

libxl: further fixups re LIBXL_DOMAIN_TYPE

* Abolish the macro LIBXL__DOMAIN_IS_TYPE which had incorrect error
  handling.  At every call site, replace it with an open-coded call to
  libxl_domain_type and check against LIBXL_DOMAIN_TYPE_INVALID.

* This involves adding an `out:' to libxl_domain_unpause.

* In libxl_domain_destroy and do_pci_add, do not `default: abort();'
  if the domain type cannot be found.  Instead switch on
  LIBXL_DOMAIN_TYPE_INVALID specifically and do some actual error
  handling.

* In libxl__primary_console_find, remove a spurious default clause
  from the domain type switch.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>