Fix the lacks of pthread_rwlock_unlock() calls.

Fix the lacks of pthread_rwlock_unlock() calls.

Two pthread_rwlock_unlock() calls are necessary if *cgroup is null
and fprintf()/fflush() fails in cgroup_attach_task_pid():

 src/api.c:785
 785             pthread_rwlock_rdlock(&cg_mount_table_lock);
 786             for(i = 0; i < CG_CONTROLLER_MAX &&
 787                             cg_mount_table[i].name[0]!='\0'; i++) {
 [snip]
 805                     ret = fprintf(tasks, "%d", tid);
 806                     if (ret < 0) {
    <<pthread_rwlock_unlock() call is necessary>>
 807                             cgroup_dbg("Error writing tid %d to
%s:%s\n",
 808                                             tid, path,
strerror(errno));
 809                             fclose(tasks);
 810                             last_errno = errno;
 811                             return ECGOTHER;
 812                     }
 813
 814                     ret = fflush(tasks);
 815                     if (ret) {
    <<pthread_rwlock_unlock() call is necessary>>
 816                             last_errno = errno;
 817                             cgroup_dbg("Error writing tid  %d to
%s:%s\n",
 818                                              tid, path,
strerror(errno));
 819                              fclose(tasks);
 820                              return ECGOTHER;
 821                      }

For the readability, this patch merges almost the same lines into one
function(__cgroup_attach_task_pid()) and adds pthread_rwlock_unlock()
call for the case the function fails.

Signed-off-by: Ken'ichi Ohmichi <oomichi@mxs.nes.nec.co.jp>
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>