Always set sys.usb.ffs.mtp.ready during configure

Sometimes, due to a race, the configure
will fail even though descriptors are actually
written because MtpServer did not die properly.
MtpServer lifetime is fixed properly in master
with multiplexed io, but to work around the
issue here, we set the property at all times.

Also reduce the timeout to leave room for
UsbDeviceManager.

Bug: 67844294
Test: Plug/replug device on sled with usb debugging off x50
Test: Verify that the race is hit, but projection still starts
Test: Verify that all other usb configurations still work
Change-Id: I39dd4d3db95e087f065d58ba80ca980559920c99