Add derived UsbTransport class with USB reset method

For testing there needs to be a way to simulate unplugging and
replugging a device. This change adds support for a USB reset
method that does this.

Also add timeouts, so USB reads/writes don't block forever
on an unresponsive device.

Test: glinux, fastboot tool still works
Test: Reset confirmed working via wireshark Linux URB captures

Change-Id: I7213a2395d4ef1c0238810e4929ab966e78c8b55