[connectionagent] Suppress errors when enabling tethering.

Enabling tethering when wlan is not powered causes it to first be
powered on. Connman will initiate a scan and may attempt to connect to
a known network. The wifi technology will then be switched to tethering
mode causing any in progress wlan connection to abort with an error
notification.

As these error notifications are expected, suppress them.
Merge pull request #74 from lpotter/master

[connectionagent] disconnect mobile data if wifi becomes ready
bump version to 0.11.11
Merge pull request #75 from amccarthy/master

[connectionagent] Suppress errors when enabling tethering.
Bump version to 0.11.12
[connectionagent] fix disconnecting mobile data when connecting to wlan

If wlan starts as unknown, it would not be favorite until it reaches
online state. Previously it would not reach the disconnecting stanza and
thus mobile data would not get disconnected.