target: check late abort from target in async_algorithm

target: check late abort from target in async_algorithm

target_run_flash_async_algorithm() ignored abort from target
(rp set to 0) when raised after all data have been written in fifo.
I could result e.g. in not reported error during flash write.

The change adds rp test after target algorithm has finished.

Change-Id: Iadd93371e4a4602737be10079479285d81ae41b2
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/3560
Tested-by: jenkins
Reviewed-by: Steven Stallion <stallion@squareup.com>
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>