Fix exception in case no hostname label is available (#255)

Author: alblasco

sdcclient/_common.py

@@ -509,7 +509,7 @@ def create_sysdig_capture(self, hostname, capture_name, duration, capture_filter
         capture_agent = None
 
         for agent in res[1]:
-            if hostname == agent['hostName']:
+            if hostname == agent.get('hostName'):
                 capture_agent = agent
                 break