rpcgen: add an XDR protocol lexer

This adds a lexer capable of handling the XDR protocol files.

The lexical rquirements are detailed in

  https://www.rfc-editor.org/rfc/rfc4506#section-6.2

pytest is introduced as a build dependancy for testing python
code.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

scripts/meson.build

@@ -37,3 +37,5 @@ foreach name : scripts
   sname = name.split('.')[0].underscorify()
   set_variable('@0@_prog'.format(sname), find_program(name))
 endforeach
+
+subdir('rpcgen')