scripts: fix API parsing of *** pointers

scripts: fix API parsing of *** pointers

The currrent generated API contains *** pointer types with bogus
whitespace in the middle:

  <arg name='keys' type='char ** *' info='pointer to a variable to store authorized keys'/>

because the tokenizer only tries to merge 2 distinct '*' together.
This refactors the code to merge an arbitrary number, resulting
in

  <arg name='keys' type='char ***' info='pointer to a variable to store authorized keys'/>

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