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/rpcgen/meson.build

@@ -0,0 +1,11 @@
+if pytest_prog.found()
+    subdir('tests')
+
+    test(
+        'rpcgen-pytest',
+        python3_prog,
+        args: [ '-mpytest' ] + rpcgen_tests,
+        env: runutf8,
+        workdir: meson.current_source_dir(),
+    )
+endif