Multipath autoreplace, control enclosure LEDs, event rate limiting

1. Enable multipath autoreplace support for FMA.

This extends FMA autoreplace to work with multipath disks.  This
requires libdevmapper to be installed at build time.

2. Turn on/off fault LEDs when VDEVs become degraded/faulted/online

Set ZED_USE_ENCLOSURE_LEDS=1 in zed.rc to have ZED turn on/off the enclosure
LED for a drive when a drive becomes FAULTED/DEGRADED.  Your enclosure must
be supported by the Linux SES driver for this to work.  The enclosure LED
scripts work for multipath devices as well.  The scripts will clear the LED
when the fault is cleared.

3. Rate limit ZIO delay and checksum events so as not to flood ZED

ZIO delay and checksum events are rate limited to 5/sec in the zfs module.

Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed by: Don Brady <don.brady@intel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #2449 
Closes #3017 
Closes #5159

include/libzfs.h

@@ -280,6 +280,9 @@ extern nvlist_t *zpool_find_vdev_by_physpath(zpool_handle_t *, const char *,
 extern int zpool_label_disk_wait(char *, int);
 extern int zpool_label_disk(libzfs_handle_t *, zpool_handle_t *, char *);
 
+int dev_is_dm(char *devname);
+char *get_underlying_path(libzfs_handle_t *hdl, char *dev_name);
+
 /*
  * Functions to manage pool properties
  */
@@ -827,10 +830,12 @@ extern int zpool_fru_set(zpool_handle_t *, uint64_t, const char *);
  */
 extern boolean_t is_mpath_whole_disk(const char *);
 extern void update_vdev_config_dev_strs(nvlist_t *);
-extern char *zfs_strip_partition(libzfs_handle_t *, char *);
+extern char *zfs_strip_partition(char *);
 
 #ifdef HAVE_LIBUDEV
 struct udev_device;
+
+extern boolean_t udev_is_mpath(struct udev_device *dev);
 extern int zfs_device_get_devid(struct udev_device *, char *, size_t);
 extern int zfs_device_get_physical(struct udev_device *, char *, size_t);
 #endif