bundles/sshmon: fix occasional KeyErrors in check_cpu_stats

bundles/sshmon/files/check_cpu_stats

@@ -5,7 +5,16 @@ from subprocess import check_output
 from sys import exit
 
 try:
-    top_output = check_output("top -b -n1 -d1 | grep -i '^\%cpu'", shell=True).decode('UTF-8').split(': ', 2)[1].strip()
+    top_output = None
+
+    for line in check_output(['top', '-b', '-n1', '-d1']).decode('UTF-8').splitlines():
+        if line.lower().strip().startswith('%cpu'):
+            top_output = line.lower().split(':', 2)[1]
+            break
+
+    if not top_output:
+        print('%cpu not found in top output')
+        exit(3)
 
     cpu_usage = {}
     for value, identifier in findall('([0-9\.\,]{3,5}) ([a-z]{2})', top_output):