Help Yorc user to understand resource allocation problems on HostPool

[adidanes]

Is your feature request related to a problem? Please describe.
In some situations an application's Compute nodes can't be allocated because of the unvailability of Hosts in the target HostPool. The unavailability can be due to the fact that some resource requirements can't be satisafied by the Hosts in the HostPool.

Describe the solution you'd like
I'd like taht Yorc tell me what requirement could not be satisfied.
The ideal would be if Yorc could inform me which requirement could not be satisfied for a given Compute of my application by a given Host in the HostPool (or by several Hosts, or even for all the Hosts)
Maybe a specific HostPool command could be created for this.