UsbDeviceManager: A better fix for race condition when starting USB accessory mode

On some devices, the USB "set configuration" command is propogated to the framework
after the "start accessory" event is received.  However, on other devices like
the 2011 ADK board, no "set configuration" command is sent at all until we have
reenumerated in acccessory mode.  To fix the original problem without breaking other
devices, we can simply remove assumptions about if or when "set configuration"
will be received.  Now we simply remain switch USB configuration to accessory mode
when we receive the "start accessory" command, and remain there until the existing
10 second timeout expires.

Bug: 13393825

Change-Id: I4c9e3423185bd7252a907e4568d9e3ff06044b7d