fix(xen-api): correct $type for records from event
fix(xen-api): correct $type for records from event

XenApi event system returns lowercased types which things difficult, for
instance, `Record#set_name_label` methods did not work for some VM
because the lib called `vm.set_name_label` instead of
`VM.set_name_label`.

To work-around this problem, a map of types from lowercased is
constructed at connection.

vatesfr/xo-web,lmcro/xo-web,lmcro/xo-web,vatesfr/xo-web,lmcro/xo-web