OsuLogin: disconnect wifi network when activitiy is destroyed

When the OsuLogin activity is killed during OSU Procedure such as
swiping it from apps list, it needs to
disconnect AP to reset provisioning flow.
Otherwise, provisioing flow is stucked in waiting for response up to
4 mins.

Bug: 124778422
Test: verified that AP is disconnected and provisioning flow is reset
when killing the application on recent app list.
Change-Id: Ic52fc9f4225bf60eb2ff10635a0659c08273b37d
Signed-off-by: Ecco Park <eccopark@google.com>