Read pool metadata once in StoragePool.getInfo()

The behavioural change of spm_id should be safe since
StoragePool.getInfo() call in  hsm.getStoragePoolInfo() is under
the (shared) pool lock making startSpm block in this host when
the info is retrieved.

Making repoStats pool independent.

Change-Id: I41a79662a4bd01fc310aa5554c38a16f3f8ba546
Signed-off-by: Eduardo <ewarszaw@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/14672
Reviewed-by: Dan Kenigsberg <danken@redhat.com>