74602: Fixes adb not seeing connected devices on Mac.

Every alternate time an adb server was started already connected devices were
not being seen. This was caused by opened usb connections being "stalled".
See this thread for more information: http://lists.apple.com/archives/usb/2011/Jun/msg00050.html

Change-Id: Ic35b7a66c3f14a837b960066557f44e105609dcb
Fixes: https://code.google.com/p/android/issues/detail?id=74602