MINOR: Do not swallow exception when collecting PIDs (#8914)

During Streams' system tests the PIDs of the Streams
clients are collected. The method the collects the PIDs
swallows any exception that might be thrown by the
ssh_capture() function. Swallowing any exceptions
might make the investigation of failures harder,
because no information about what happened are recorded.

Reviewers: John Roesler <vvcephei@apache.org>

tests/kafkatest/services/streams.py

@@ -17,6 +17,7 @@ import os.path
 import signal
 import streams_property
 import consumer_property
+from ducktape.cluster.remoteaccount import RemoteCommandError
 from ducktape.services.service import Service
 from ducktape.utils.util import wait_until
 from kafkatest.directory_layout.kafka_path import KafkaPathResolverMixin
@@ -215,8 +216,10 @@ class StreamsTestBaseService(KafkaPathResolverMixin, JmxMixin, Service):
 
     def pids(self, node):
         try:
-            return [pid for pid in node.account.ssh_capture("cat " + self.PID_FILE, callback=int)]
-        except:
+            pids = [pid for pid in node.account.ssh_capture("cat " + self.PID_FILE, callback=str)]
+            return [int(pid) for pid in pids]
+        except Exception, exception:
+            self.logger.debug(str(exception))
             return []
 
     def stop_nodes(self, clean_shutdown=True):