Add additional HBA information to sr-probe and sr-create

There currently is no easy way to gather basic information about HBAs, which
are required for the provisioning of external storage, without accessing Dom0.

This commit adds some basic information about the availiable FC and iSCSI HBAs
to the HBA-specific output of "xe-srobe type=LVMoHBA" and "xe-create
type=LVMoHBA" to address this gap. It does this by including the contents of
all fc_host and iscsi_host class specific files.

Signed-off-by: Robert Breker <robert.breker@citrix.com>