common: implement an explicit preference order in sambacc installation

[obnoxxx]

this explicitly implements a preference order for sambacc
custom installation sources like so:

local repo ->  -> rpm ->  wheel   -> copr.

It makes the output a bit more verbose while at it.
overall, the behavior of the sambacc installation is made a bit more consistent and predictable

[obnoxxx]

@phlogistonjohn : the requests you had on a previous version of this patch in #193 have all been addressed

[phlogistonjohn]

I think this has (unintentionally) inverted the priority of the various installation sources. Previously, if it found a wheel and then an rpm it would "prefer" the RPM. Now, AFAICT it will find a wheel and stop looking for anything else, implicitly preferring the wheel.

I strongly recommend undoing the restructuring of the if blocks so that every if block still gets visited and the various log lines can be emitted. Then after the sequence of if-blocks you can log the state of action to indicate what the 'preferred' action is going to be.

[obnoxxx]

@phlogistonjohn wrote:

I think this has (unintentionally) inverted the priority of the various installation sources. Previously, if it found a wheel and then an rpm it would "prefer" the RPM. Now, AFAICT it will find a wheel and stop looking for anything else, implicitly preferring the wheel.

Indeed, this analysis is correct and it was not intentional.

I strongly recommend undoing the restructuring of the if blocks so that every if block still gets visited and the various log lines can be emitted. Then after the sequence of if-blocks you can log the state of action to indicate what the 'preferred' action is going to be.

I have changed it this way now, making the original preference order explicit instead of reverting it.

[phlogistonjohn]

lgtm, thanks