Stop deploying SDKs with OmniSharp

[DustinCampbell]

Fixes #765

This change stops deploying the .NET Core MSBuild SDKs with OmniSharp. That was a stop gap for .NET Core 1.0. However, with .NET Core 2.0 around the corner, it's time to stop deploying them and rely on the .NET Core SDK installed on the user's machine.

To locate the correct .NET Core SDK, we simply launch dotnet --info in the working directory of the project. That should properly handle the case where the SDK is specified in a global.json file. Then, we process the text returned by dotnet --info and locate the "Base Path" value. Combining this with "Sdks" should be the correct value.

[DustinCampbell]

Note, this also shrinks the drops by a good bit.

[filipw]

very nice! also the build script should be faster

On a side note, I think we should also review what is the role of OmniSharp.Abstractions. At the moment it's a mix of a little of everything i.e. config class with hardcoded Roslyn versions or endpoint paths, all the request/response models, a bunch of interfaces, a bunch of extension methods and utilities, CLI wrapper like theDotNetCliService etc.

[DustinCampbell]

Yes. I've been going through Abstractions and moving things out. For example, a lot of implementations have moved to OmniSharp.Host and OmniSharp.Roslyn.

[DustinCampbell]

also the build script should be faster

Not by much. Restoring these packages and copying their contents was a fairly small amount of time compared to other steps, like publish.

[juergenhoetzel]

I use -use-global-dotnet-sdk but the non-existing local SDK path is still referenced in the msbuild.sh script:
msbuild.sh: line 3: cd: ./.dotnet/sdk/1.0.1/: No such file or directory

[juergenhoetzel]

There is an Enviroment property in RunOptions:

    public IDictionary<string, string> Environment { get; }

using this property, the actual SDK_DIR could be passed to msbuild.sh?

[DustinCampbell]

Yes, this should be done. I'm not sure what your comment has to do with this particular PR though. msbuild.sh was added awhile ago.

[juergenhoetzel]

Yes, this should be done. I'm not sure what your comment has to do with this particular PR though. msbuild.sh was added awhile ago.

I thought the functionality of passing the correct SDK_DIR to msbuild.sh should have been part of this PR, because building on GNU/Linux systems fails if you use this new feature (dont deploy SDK).