Dump unique configurations and Uberblocks in zdb -lu

Dump unique configurations and Uberblocks in zdb -lu

For zdb -l, detect when the configuration nvlist in some label l (l>0)
is the same as a configuration already dumped.  If so, do not dump it.

Make a similar check when dumping Uberblocks for zdb -lu.  Check whether
a label already dumped contains an identical Uberblock.  If so, do not
dump the Uberblock.

When dumping a configuration or Uberblock, state which labels it is
found in (0-3), for example: labels = 1 2 3

Detecting redundant uberblocks or configurations is accomplished by
calculating checksums of the uberblocks and the packed nvlists
containing the configuration.

If there is nothing unique to be dumped for a label (ie the
configuration and uberblocks have checksums matching those already
dumped) print nothing for that label.

With additional l's or u's, increase verbosity as follows:

-l      Dump each unique configuration only once.
        Indicate which labels it appears in.
-ll     In addition, dump label space usage stats.
-lll    Dump every configuration, unique or not.

-u      Dump each unique, valid, uberblock only once.
        Indicate which labels it appears in.
-uu     In addition, state which slots are invalid.
-uuu    Dump every uberblock, unique or not.
-uuuu   Dump the uberblock blockpointer (used to be -uuu)

Make exit values conform to the manual page.  Failing to unpack a
configuration nvlist is considered an error, as well as failing to open
or read from the device.

Add three tests, zdb_00{3,4,5}_pos to verify the above functionality.

An example of the output:
	------------------------------------
	LABEL 0
	------------------------------------
	    version: 5000
	    name: 'pool'
	    state: 1
	    txg: 880
	    < ... redacted ... >
	    features_for_read:
		com.delphix:hole_birth
		com.delphix:embedded_data
	    labels = 0
	    Uberblock[0]
		magic = 0000000000bab10c
		version = 5000
		txg = 0
		guid_sum = 3038694082047428541
		timestamp = 1487715500 UTC = Tue Feb 21 14:18:20 2017
		labels = 0 1 2 3
	    Uberblock[4]
		magic = 0000000000bab10c
		version = 5000
		txg = 772
		guid_sum = 9045970794941528051
		timestamp = 1487727291 UTC = Tue Feb 21 17:34:51 2017
		labels = 0
	    < ... redacted ... >
	------------------------------------
	LABEL 1
	------------------------------------
	    version: 5000
	    name: 'pool'
	    state: 1
	    txg: 14
	    < ... redacted ... >
		com.delphix:embedded_data
	    labels = 1 2 3
	    Uberblock[4]
		magic = 0000000000bab10c
		version = 5000
		txg = 4
		guid_sum = 7793930272573252584
		timestamp = 1487727521 UTC = Tue Feb 21 17:38:41 2017
		labels = 1 2 3
	    < ... redacted ... >

Reviewed-by: Tim Chase <tim@chase2k.com>
Reviewed-by: Don Brady <don.brady@intel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes #5738