Adopt pyzfs from ClusterHQ

This commit introduces several changes:

 * Update LICENSE and project information

 * Give a good PEP8 talk to existing Python source code

 * Add RPM/DEB packaging for pyzfs

 * Fix some outstanding issues with the existing pyzfs code caused by
   changes in the ABI since the last time the code was updated

 * Integrate pyzfs Python unittest with the ZFS Test Suite

 * Add missing libzfs_core functions: lzc_change_key,
   lzc_channel_program, lzc_channel_program_nosync, lzc_load_key,
   lzc_receive_one, lzc_receive_resumable, lzc_receive_with_cmdprops,
   lzc_receive_with_header, lzc_reopen, lzc_send_resume, lzc_sync,
   lzc_unload_key, lzc_remap

Note: this commit slightly changes zfs_ioc_unload_key() ABI. This allow
to differentiate the case where we tried to unload a key on a
non-existing dataset (ENOENT) from the situation where a dataset has
no key loaded: this is consistent with the "change" case where trying
to zfs_ioc_change_key() from a dataset with no key results in EACCES.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #7230

lib/libzfs/libzfs_crypto.c

@@ -1185,7 +1185,7 @@ zfs_crypto_unload_key(zfs_handle_t *zhp)
 	if (keystatus == ZFS_KEYSTATUS_UNAVAILABLE) {
 		zfs_error_aux(zhp->zfs_hdl, dgettext(TEXT_DOMAIN,
 		    "Key already unloaded for '%s'."), zfs_get_name(zhp));
-		ret = ENOENT;
+		ret = EACCES;
 		goto error;
 	}
 
@@ -1198,7 +1198,7 @@ zfs_crypto_unload_key(zfs_handle_t *zhp)
 			zfs_error_aux(zhp->zfs_hdl, dgettext(TEXT_DOMAIN,
 			    "Permission denied."));
 			break;
-		case ENOENT:
+		case EACCES:
 			zfs_error_aux(zhp->zfs_hdl, dgettext(TEXT_DOMAIN,
 			    "Key already unloaded for '%s'."),
 			    zfs_get_name(zhp));