ui: Use XkbGetMap and XkbGetNames instead of XkbGetKeyboard

XkbGetKeyboard does not work in XWayland and even on non-Wayland
X11 servers its use is discouraged:

  https://bugs.freedesktop.org/show_bug.cgi?id=89240



This resolves a problem whereby QEMU prints

  "could not lookup keycode name"

on startup when running under XWayland. Keymap handling is
however still broken after this commit, since Xwayland is
reporting a keymap we can't handle

  "unknown keycodes `(unnamed)', please report to qemu-devel@nongnu.org"

NB, native Wayland support (which is the default under GTK3) is
not affected - only XWayland (which can be requested with GDK_BACKEND
on GTK3, and is the only option for GTK2).

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170227132343.30824-1-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>