storage: Fix autostart of pool with "fc_host" type adapter

storage: Fix autostart of pool with "fc_host" type adapter

The "checkPool" is a bit different for pool with "fc_host"
type source adapter, since the vHBA it's based on might be
not created yet (it's created by "startPool", which is
involked after "checkPool" in storageDriverAutostart). So it
should not fail, otherwise the "autostart" of the pool will
fail either.

The problem is easy to reproduce:
    * Enable "autostart" for the pool
    * Restart libvirtd service
    * Check the pool's state