Fix gcc uninitialized variable warnings

Gcc -Wall warn: 'uninitialized variable'

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>

lib/libzfs/libzfs_dataset.c

@@ -1362,7 +1362,7 @@ zfs_prop_set(zfs_handle_t *zhp, const char *propname, const char *propval)
 	zfs_prop_t prop;
 	boolean_t do_prefix;
 	uint64_t idx;
-	int added_resv;
+	int added_resv = 0;
 
 	(void) snprintf(errbuf, sizeof (errbuf),
 	    dgettext(TEXT_DOMAIN, "cannot set property for '%s'"),
@@ -2791,7 +2791,7 @@ zfs_create_ancestors(libzfs_handle_t *hdl, const char *path)
 {
 	int prefix;
 	char *path_copy;
-	int rc;
+	int rc = 0;
 
 	if (check_parents(hdl, path, NULL, B_TRUE, &prefix) != 0)
 		return (-1);
@@ -3348,8 +3348,8 @@ zfs_rollback(zfs_handle_t *zhp, zfs_handle_t *snap, boolean_t force)
 	int err;
 	zfs_cmd_t zc = { "\0", "\0", "\0", "\0", 0 };
 	boolean_t restore_resv = 0;
-	uint64_t old_volsize, new_volsize;
-	zfs_prop_t resv_prop;
+	uint64_t old_volsize = 0, new_volsize;
+	zfs_prop_t resv_prop = { 0 };
 
 	assert(zhp->zfs_type == ZFS_TYPE_FILESYSTEM ||
 	    zhp->zfs_type == ZFS_TYPE_VOLUME);
@@ -3579,6 +3579,7 @@ zfs_rename(zfs_handle_t *zhp, const char *target, boolean_t recursive)
 			    "child dataset with inherited mountpoint is used "
 			    "in a non-global zone"));
 			(void) zfs_error(hdl, EZFS_ZONED, errbuf);
+			ret = -1;
 			goto error;
 		}
 

lib/libzfs/libzfs_import.c

@@ -434,7 +434,7 @@ get_configs(libzfs_handle_t *hdl, pool_list_t *pl, boolean_t active_ok)
 	pool_entry_t *pe;
 	vdev_entry_t *ve;
 	config_entry_t *ce;
-	nvlist_t *ret = NULL, *config = NULL, *tmp, *nvtop, *nvroot;
+	nvlist_t *ret = NULL, *config = NULL, *tmp = NULL, *nvtop, *nvroot;
 	nvlist_t **spares, **l2cache;
 	uint_t i, nspares, nl2cache;
 	boolean_t config_seen;

lib/libzfs/libzfs_util.c

@@ -956,7 +956,7 @@ zprop_print_one_property(const char *name, zprop_get_cbdata_t *cbp,
     const char *source, const char *recvd_value)
 {
 	int i;
-	const char *str;
+	const char *str = NULL;
 	char buf[128];
 
 	/*