Fix broken ps.top

This fixes two problems:

1. Poorly-designed handling of unpacking selective items from a
   `psutil.Process` instance, leading to ValueError. This is fixed by
   slicing.

2. `psutil.Process` objects are not sortable on Python 3. Fixed by using
   a key lambda to sort on the `pid` attribute.

salt/modules/ps.py

@@ -147,26 +147,22 @@ def top(num_processes=5, interval=3):
     for pid in psutil.pids():
         try:
             process = psutil.Process(pid)
-            user, system = process.cpu_times()
-        except ValueError:
-            user, system, _, _ = process.cpu_times()
         except psutil.NoSuchProcess:
             continue
+        else:
+            user, system = process.cpu_times()[:2]
         start_usage[process] = user + system
     time.sleep(interval)
     usage = set()
     for process, start in six.iteritems(start_usage):
-        try:
-            user, system = process.cpu_times()
-        except ValueError:
-            user, system, _, _ = process.cpu_times()
-        except psutil.NoSuchProcess:
-            continue
+        user, system = process.cpu_times()[:2]
         now = user + system
         diff = now - start
         usage.add((diff, process))
 
-    for idx, (diff, process) in enumerate(reversed(sorted(usage))):
+    for idx, (diff, process) in enumerate(
+        sorted(usage, key=lambda x: x[1].pid, reverse=True)
+    ):
         if num_processes and idx >= num_processes:
             break
         if len(_get_proc_cmdline(process)) == 0:

tests/unit/modules/test_ps.py

@@ -310,6 +310,15 @@ class PsTestCase(TestCase):
                 ps.get_users()[0],
             )
 
+    def test_top(self):
+        """
+        There's no need to do any asserts here. Merely running the function
+        should not raise a traceback. See the following issue:
+
+        https://github.com/saltstack/salt/issues/56942
+        """
+        ps.top()
+
         ## This is commented out pending discussion on https://github.com/saltstack/salt/commit/2e5c3162ef87cca8a2c7b12ade7c7e1b32028f0a
         # @skipIf(not HAS_UTMP, "The utmp module must be installed to run test_get_users_utmp()")
         # @patch('salt.utils.psutil_compat.get_users', new=MagicMock(return_value=None))  # This will force the function to use utmp