This allows the caller to specify a uid and gid to use, even if there
is no corresponding password entry. This will be useful in certain
Xen configurations.
We don't support just -runas <uid> because: (i) deprivileging without
calling setgroups would be ineffective (ii) given only a uid we don't
know what gid we ought to use (since uids may eppear in multiple
passwd file entries with different gids).
Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com> Reviewed-by: Anthony PERARD <anthony.perard@citrix.com> CC: Paolo Bonzini <pbonzini@redhat.com> CC: Markus Armbruster <armbru@redhat.com> CC: Daniel P. Berrange <berrange@redhat.com> CC: Michael Tokarev <mjt@tls.msk.ru> Reviewed-by: Markus Armbruster <armbru@redhat.com>