Update __init__.py

This is in regards to the issue - Example code issue golismero#14

We are receiving this problem due to referencing a port number that is already in use. That is the reason we are getting this error.  I have added the outputs under the issue section.

openvas_lib/__init__.py

@@ -501,6 +501,8 @@ def __init__(self, host, user, password, port=9390, timeout=None, ssl_verify=Fal
 			raise VulnscanAuthFail("Error while trying to authenticate into the server.")
 		except RemoteVersionError:
 			raise VulnscanVersionError("Invalid OpenVAS version in remote server.")
+		except ValueError:
+			raise ValueError('Invalid Argument Call')
 
 		#
 		# Flow control