stlink: Add workaround for intermittent FW info retrieval failure

stlink: Add workaround for intermittent FW info retrieval failure

It appears that on some host USB configurations(2012 MacBook Air)
multiple restarts of openocd tool cause the FW on STLINKv2 dongle to
go into a weird state in which it will no longer respond to
STLINK_GET_VERSION command. This patch adds code that, if said request
fails for the first time, attempts to reset the device and retry to
initialize it and obtain FW information one more time.

Change-Id: I7227fc972adb49d52ae700ad48ab9f66b2aaa72c
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Reviewed-on: http://openocd.zylin.com/1561
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>