avoid redundant domain produce() in createStoragePool

As the domains in hsm.createStoragePool are going to
be accessed much later, and may loose validity till then.
Just produce from cache and check the validity when actully use it.

Change-Id: If1c236aa3043068ca8f3f376cb340e986cd484bb
Signed-off-by: Adam Litke <alitke@redhat.com>