Add exception handling for the API version parsing

I have added try-except clauses in order to prevent the process from
crashing if a non-parsable integer is used for the api_version option.

Signed-off-by: Konrad Reiche <konrad.reiche@fokus.fraunhofer.de>

ckanext/harvest/harvesters/base.py

@@ -130,7 +130,11 @@ class HarvesterBase(SingletonPlugin):
 
             # Check API version
             if self.config:
+                try:
                     api_version = int(self.config.get('api_version', 2))
+                except ValueError:
+                    raise ValueError('api_version must be an integer')
+
                 #TODO: use site user when available
                 user_name = self.config.get('user', u'harvest')
             else:

ckanext/harvest/harvesters/ckanharvester.py

@@ -53,7 +53,10 @@ class CKANHarvester(HarvesterBase):
             self.config = json.loads(config_str)
 
             if 'api_version' in self.config:
+                try:
                     self.api_version = int(self.config['api_version'])
+                except ValueError:
+                    raise ValueError('api_version must be an integer')
 
             log.debug('Using config: %r', self.config)
         else: