Fix 'zpool create -t <tempname>'

Fix 'zpool create -t <tempname>'

Creating a pool with a temporary name fails when we also specify custom
dataset properties: this is because we mistakenly call
zfs_set_prop_nvlist() on the "real" pool name which, as expected,
cannot be found because the SPA is present in the namespace with the
temporary name.

Fix this by specifying the correct pool name when setting the dataset
properties.

Reviewed-by: Prakash Surya <prakash.surya@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #7502
Closes #7509