CP-23026 pool join: consider also product version and product_brand
CP-23026 pool join: consider also product version and product_brand

This commit adds a generic function to compare versions across local
host and pool master and employs it to compare product version and
product brand as part of the checks before a host can join a pool.

Signed-off-by: Christian Lindig <4f88b50bc9dba63c9a7d9e208d4b3ac6f1a52800@citrix.com>

srowe/xen-api,euanh/xen-api,srowe/xen-api,srowe/xen-api,euanh/xen-api,euanh/xen-api,euanh/xen-api,srowe/xen-api,euanh/xen-api,euanh/xen-api,srowe/xen-api