Alarm validation against inventory is too strict

[jktjkt]

The RFC defines some extra rules when matching the resource against the inventory and the shelving rules:

• XPath rules should be supported (which means that, e.g., the inventory might contain a resource set to the XPath /ietf-interfaces:interfaces/ietf-interfaces:interface[ietf-interfaces:type='ianaift:ethernetCsmacd'], and then we should recognize that this matches when fed with, e.g., /if:interfaces/if:interface[if:name='eth1']). This will be rather expensive because any alarm would require fetching arbitrary content of the operational DS (with bonus points in case the XPath refers to the ietf-alarms module :) ). As a minimal fix, we should relax the inventory validation so that it doesn't reject these alarms, but I think that we will have to fetch everything so that we can implement shelving properly.
• The yang:object-identifier should be implemented as a prefix match (TODO when implementing this: also catch derived types).
• If it's an UUID or a string (and there's no difference between these on the YANG type level, apparently!), then it's supposed to be a regular expression.

Right now we are comparing strings for equality, which is a wrong thing to do.