modules/zpool : make it available for compatible Solaris family

The whole module has been reviewed for a better compliance with Salt and now
Solaris (> 5.9) / SmartOS can use it. Some commands have been simplified and
the idea is to provide another module for the 'zfs' command support.
modules/zpool : add check for FreeBSD and complete doc
modules/zpool : make use of memoize
pull #5144 : use built-in set instead of list
Merge remote-tracking branch 'upstream/develop' into module_zpool
Merge pull request #5144 from virtua-network/module_zpool

modules/zpool : make it available for compatible Solaris family