Allow RPC to target non-master personas

[Amir Kamil]

Currently, an RPC can only target the master persona on a remote rank. In order to target a different persona, an RPC must be sent to the master persona, which would then have to enqueue the work on the target persona through an LPC. This adds an extra scheduling step, and it also requires the user to build some sort of application-specific naming for personas.

Instead, we should consider providing an API for persona naming, as well as flavors of RPC that target specific personas.

Allowing non-master personas to be targeted may also allow us to take advantage of GASNet-EX endpoints.

[Dan Bonachea]

This issue was triaged at the 2018-06-13 Pagoda meeting and assigned a new milestone/priority.

It was noted this would be a major semantic departure from our current RPC design, implying non-trivial spec additions and significant implementation effort.

In particular, if the feature was intended to internally leverage GEX endpoints it would require collective coordination to allocate resources and establish global naming for non-master personas.