7391 FIX mk_mongodb: don't crash upon missing flushing info

The plugin no longer crashes the server does not report info
on 'backgroundFlushing', as is the case for MongoDB 4.0 onwards.

CMK-1885

Change-Id: Ieda32ee6d42645e1ce06fee1c20d30141abbad4f

.werks/7391

@@ -0,0 +1,11 @@
+Title: mk_mongodb: don't crash upon missing flushing info
+Level: 1
+Component: checks
+Compatible: compat
+Edition: cre
+Version: 1.6.0i1
+Date: 1554298869
+Class: fix
+
+The plugin no longer crashes the server does not report info
+on 'backgroundFlushing', as is the case for MongoDB 4.0 onwards.

agents/plugins/mk_mongodb

@@ -18,6 +18,17 @@ import time
 import pymongo  # pylint: disable=import-error
 
 
+def section_flushing(server_status):
+    # key is depricated for MongoDB 4.0
+    flushing_info = server_status.get("backgroundFlushing")
+    if flushing_info is None:
+        return
+    sys.stdout.write("<<<mongodb_flushing>>>\n")
+    sys.stdout.write("average_ms %s\n" % flushing_info["average_ms"])
+    sys.stdout.write("last_ms %s\n" % flushing_info["last_ms"])
+    sys.stdout.write("flushed %s\n" % flushing_info["flushes"])
+
+
 def main():  # pylint: disable=too-many-branches,too-many-locals
     # might be implemented in the future..
     host = None
@@ -110,10 +121,7 @@ def main():  # pylint: disable=too-many-branches,too-many-locals
                 for key, value in global_lock_info[what].items():
                     sys.stdout.write("%s %s %s\n" % (what, key, value))
 
-    sys.stdout.write("<<<mongodb_flushing>>>\n")
-    sys.stdout.write("average_ms %s\n" % server_status["backgroundFlushing"]["average_ms"])
-    sys.stdout.write("last_ms %s\n" % server_status["backgroundFlushing"]["last_ms"])
-    sys.stdout.write("flushed %s\n" % server_status["backgroundFlushing"]["flushes"])
+    section_flushing(server_status)
 
     # Unused
     # server_version = tuple(con.server_info()['version'].split('.'))