jsonrpc: StoragePool connect missing default value

DomainsMap argument is defined in schema as optional but it is missing
default value.

Change-Id: Ibb5923e60314993834cf005af4ad89c21dd0dd76
Signed-off-by: pkliczewski <piotr.kliczewski@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/24641
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>