jtag: enable connect under reset

jtag: enable connect under reset

Currently if the target supports srst_nogate we wait until target assert_reset
until we get a chance to assert the srst.
However sometimes we will not get this far if the target has already failed
the jtag_examine_chain.

This has been tested on targets that support this behaviour (STM32 and STR9).

Change-Id: Ibcf7584b137b472f31ba6ddd5cd99d848c5508d1
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/971
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>