Convert XenAPI platform values to appropriate types.

Convert XenAPI platform values to appropriate types.

XenAPI defines the platform attribute of a VM as a string-string map
but in various code paths in xend the platform entries are expected to be
another type, e.g. int.  This patch defines the types of each platform
entry and converts the entry values to appropriate type when new domU
configuration is created via XenAPI.

Alternatively the values could be casted to appropriate type when used
but seems prudent to do the conversion when domU configuration is
created.

Signed-off-by: Jim Fehlig <jfehlig@novell.com>