Fix test When_type_is_in_NuGet_then_xml_docs_should_be_found and tests in Namotion.Reflection.Cecil.Tests (Linux)

[Apollo3zehn]

Related to #33.

With the change suggested in comment #33 (comment) I am able to make the previously failing NuGet test succeed on Linux (When_type_is_in_NuGet_then_xml_docs_should_be_found).

Tests in Namotion.Reflection.Cecil.Tests are also now executed successfully:

[Apollo3zehn]

I added another commit to also find the XML docs when using the artifacts output layout.

I also had to slightly modify the regex which tries to extract nuget package paths from the project.nuget.cache file. My file has the following line:

"/home/vincent/.nuget/packages/nexus.sources.structuredfile/2.0.0-beta.38/nexus.sources.structuredfile.2.0.0-beta.38.nupkg.sha512"

This is incompatible with the previously used string interpolation value assemblyName.Version.ToString(3). I replaced that one by .*?, i.e. a non-greedy match-all. This works because there will never be two versions of the same package.