Have device_identifiers() return a struct instead of a tuple

[mulkieran]

The struct should have two fields for the two identifiers and I don't think it needs any impl.

It can be used in the definition of the StaticHeader struct and also used in the result type of functions that call device_identifiers().

This should reduce type complexity and eliminate confusion in a few places.

It should wait until I've gotten in the PR that eliminates the device.rs module that defines DevOwnership, though, because that'll get rid of some invocations of device_identifiers.

[mulkieran]

Call it StratisIdentifiers and define it in static_header.rs? Start out by just defining the method device_identifiers so that it returns StratisResult<Option<StratisIdentifiers>> and then do the right thing wherever that method is used.

[mulkieran]

Best to not touch until #1809 gets in.

[mulkieran]

@GuillaumeGomez, I think this would be a good one, but we'ld like to get #1809 merged first.

[GuillaumeGomez]

Sounds good to me. Please ping me once #1809 is merged.

[mulkieran]

@GuillaumeGomez Please feel free to begin at any time.

[GuillaumeGomez]

Ok!