target: fix memory leaks on target_create() fail

target: fix memory leaks on target_create() fail

There are failure cases of target_create() that are not checked.
Plus, in case of failure the memory allocated in not properly
released before returning error.

Check all the possible failure in target_create().
Change current_target only when target is successfully created.
Add the new target to all_targets list only when target is
successfully created.
Release all the allocated memory before quit on failure.
Use malloc() instead of calloc() for target->type, because the
struct will be fully populated with memcpy().

Change-Id: Ib6f91cbb50c28878e7c73dc070b17b8d7d4e902f
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5776
Tested-by: jenkins