helper/command: do not capture log in script_command_run()

helper/command: do not capture log in script_command_run()

Command's output should be put in JimTcl result.
We should not anymore capture the log output and pack it as a
JimTcl result.

Remove the log capture feature in script_command_run().

This change was part of http://openocd.zylin.com/1815 from Paul
Fertser and has been extracted and rebased to simplify the review.

Change-Id: Id326c8719e1cee9156d7fc15ae8355ec79a74951
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5085
Tested-by: jenkins