target: reexamine after polling succeeds again

target: reexamine after polling succeeds again

If polling was failing, it likely meant that either the target was
disconnected or rebooted. In the latter case it needs to be reexamined
to be properly configured for the debug session, so do it just in
case.

Reported-by: Tim Sander <tim@krieglstein.org>
Tested-by: Tim Sander <tim@krieglstein.org>
Change-Id: I5b067c18d9276d4e86cc59739f196ae7d0931622
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2151
Tested-by: jenkins
Reviewed-by: Tim Sander <tim@krieglstein.org>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>