MB-45684: Fix cbstats stats_key and stats_vkey error messages

The exception is now printed rather than hitting an AttributeError.

e.g.,

 Memcached error #1:  KEY_ENOENT : Not Found :

Rather than the previous:

Traceback (most recent call last):
  File ".../engines/ep/management/cbstats", line 539, in stats_key
    vbs = mc.stats(cmd)
  File ".../engines/ep/management/mc_bin_client.py", line 636, in stats
    cmd, opaque, cas, klen, extralen, data = self._handleKeyedResponse(None)
  File ".../engines/ep/management/mc_bin_client.py", line 292, in _handleKeyedResponse
    raise MemcachedError(errcode,  msg)
mc_bin_client.ErrorKeyEnoent: Memcached error #1:  KEY_ENOENT : Not Found :

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File ".../engines/ep/management/cbstats", line 1010, in <module>
    main()
  File ".../engines/ep/management/cbstats", line 1007, in main
    c.execute()
  File ".../engines/ep/management/clitool.py", line 83, in execute
    f[0](mc, *args[2:], **opts.__dict__)
  File ".../engines/ep/management/cbstats", line 49, in g
    f(*args, **kwargs)
  File ".../engines/ep/management/cli_auth_utils.py", line 106, in g
    f(*args, **kwargs)
  File ".../engines/ep/management/cbstats", line 541, in stats_key
    print(e.message)
AttributeError: 'ErrorKeyEnoent' object has no attribute 'message'

Change-Id: Iae887189b485e1c62dd5f5ceba599e0660502067
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/151234
Reviewed-by: Daniel Owen <[email protected]>
Tested-by: James Harrison <[email protected]>
Tested-by: Build Bot <[email protected]>

engines/ep/management/cbstats

@@ -538,7 +538,7 @@ def stats_key(mc, key, vb, *args):
         print(cmd)
         vbs = mc.stats(cmd)
     except mc_bin_client.MemcachedError as e:
-        print(e.message)
+        print(e)
         sys.exit(1)
     except ValueError as e:
         print("Failed to parse collection: %s" % str(e))
@@ -563,7 +563,7 @@ def stats_vkey(mc, key, vb, *args):
         cmd = "%s %s %s %s" % (requestStatKey, key, str(vb), collection)
         vbs = mc.stats(cmd)
     except mc_bin_client.MemcachedError as e:
-        print(e.message)
+        print(e)
         sys.exit(1)
     except ValueError as e:
         print("Failed to parse collection: %s" % str(e))