iFixes #15 - nmap parser fixed and working!

self.port_service_cpe was being deleted but still needed later, replaced
del with reassignment of "".

Dived into old skaldship/nmap.py fixes that somehow didn't make it over
to release code.
Merge pull request #17 from grutz/nmap_fix

Fixes #15 - nmap parser fixed and working! thanks @felmoltor and @hybriz