Don't assume string params to Install are identifiers

[HebaruSan]

Problem

CmdLine's ckan install identifier=version syntax is broken:

$ ../CKAN/_build/ckan install Astrogator=v0.9.0
About to install...


Continue? [Y/n]

(The list of modules to install is missing.)

This also affects the ckan install -c localfile.ckan syntax:

$ ../CKAN/_build/ckan install -c KerbalAircraftExpansion-3-2.8.0.1.ckan
About to install...


Continue? [Y/n]

Which also breaks pull request validation:

https://ci.ksp-ckan.space/job/NetKAN/8294/console

Running ckan install -c built/KerbalAircraftExpansion-3-2.8.0.1.ckan
About to install...



Updating registry
Committing filesystem changes
Rescanning GameData
Done!

(Nothing gets installed.)

Noticed while checking validation of KSP-CKAN/NetKAN#7194.

Cause

This line from #2753 assumed that the list of strings passed to InstallList are pure identifiers:

CKAN/Core/ModuleInstaller.cs

Line 140 in 8eabff4

InstallList(resolver.ModList().Where(m => modules.Contains(m.identifier)).ToList(), options, downloader);

But they can include the version as well, so comparing them to identifiers doesn't work as intended.

Changes

Now instead of checking that the module's identifier is present in the parameter list, we check that the resolver's ReasonFor is UserRequested. This has the intended effect of passing only CkanModules that were specified in the parameters (so the rest can be flagged as auto-installed), but does not break the identifier=version syntax.

And since it's kind of shocking that functionality this important broke and no one noticed, a new ModuleInstaller test is added for the identifier=version syntax, which fails on master and passes on this branch.