3954 metaslabs continue to load even after hitting zfs_mg_alloc_failure limit
4080 zpool clear fails to clear pool
4081 need zfs_mg_noalloc_threshold
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>

*** 5403,5413 ****
  
          zfs_ioctl_register_pool(ZFS_IOC_POOL_IMPORT, zfs_ioc_pool_import,
              zfs_secpolicy_config, B_TRUE, POOL_CHECK_NONE);
  
          zfs_ioctl_register_pool(ZFS_IOC_CLEAR, zfs_ioc_clear,
!             zfs_secpolicy_config, B_TRUE, POOL_CHECK_SUSPENDED);
          zfs_ioctl_register_pool(ZFS_IOC_POOL_REOPEN, zfs_ioc_pool_reopen,
              zfs_secpolicy_config, B_TRUE, POOL_CHECK_SUSPENDED);
  
          zfs_ioctl_register_dataset_read(ZFS_IOC_SPACE_WRITTEN,
              zfs_ioc_space_written);
--- 5403,5413 ----
  
          zfs_ioctl_register_pool(ZFS_IOC_POOL_IMPORT, zfs_ioc_pool_import,
              zfs_secpolicy_config, B_TRUE, POOL_CHECK_NONE);
  
          zfs_ioctl_register_pool(ZFS_IOC_CLEAR, zfs_ioc_clear,
!             zfs_secpolicy_config, B_TRUE, POOL_CHECK_NONE);
          zfs_ioctl_register_pool(ZFS_IOC_POOL_REOPEN, zfs_ioc_pool_reopen,
              zfs_secpolicy_config, B_TRUE, POOL_CHECK_SUSPENDED);
  
          zfs_ioctl_register_dataset_read(ZFS_IOC_SPACE_WRITTEN,
              zfs_ioc_space_written);