apps: add DisconnectReason to netlog summary

Shill now processes DisconnectReason property updates from supplicant.
These log lines will now be highlighted in the shill log processor.

Sample line from log:
[2015-07-14T20:35:50.708693+00:00] [94:16:21.598] WiFi wlan0 supplicant
updated DisconnectReason -4

The log line will appear in the manager summary and will be highlighted
in the log text.

BUG=chromium:510182
TEST=checked manually and ran "grunt test"

Change-Id: I39e78e725319fe79d6f83ed35e7c9701f2c92d9c
1 file changed