tests/redpanda: do not include command with no args into pid list

When `ps` is unable to determine process arguments it wraps the command
name in square brackets like this:
```
262250 pts/278  R+     0:00 [redpanda]
```

this was incorrectly interpreted as running Redpanda, the node was never
brought back up.
Fixed issue by filtering out incorrect `ps` output lines.

Fixes: redpanda-data#8753

Signed-off-by: Michal Maslanka <[email protected]>

tests/rptest/services/redpanda.py

@@ -2086,7 +2086,7 @@ def remove_local_data(self, node):
 
     def redpanda_pid(self, node):
         try:
-            cmd = "ps ax | grep -i 'redpanda' | grep -v grep | grep -v 'version' | awk '{print $1}'"
+            cmd = "ps ax | grep -i 'redpanda' | grep -v grep | grep -v 'version'| grep -v \"]\" | awk '{print $1}'"
             for p in node.account.ssh_capture(cmd,
                                               allow_fail=True,
                                               callback=int):