[xharness] Use msbuild for some tests

[VincentDondain]

• Removed new string [] { "Import", "Project" }, which is causing issues when using msbuild (hopefully it's not breaking things since we're mostly using msbuild now).

[VincentDondain]

This PR is a tentative at using msbuild for our test. It needs to be tested on the bots since their setup is different than local setup (where those changes work).

[monojenkins]

Build failure

!!! Couldn't read commit file !!!

[VincentDondain]

I hoped this PR might work on the bots as it works locally but it seems to be hitting issues due to lack of msbuild redirect.

In the tests build logs we can see a mix of /Users/builder/jenkins/workspace/xamarin-macios-pr-builder/_ios-build/Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/* and /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/lib/mono/Xamarin.iOS/* which breaks.

Might be due in part or in full to MSBuildExtensionsPath=null which is defined when using msbuild. However using something else doesn't seem to be supported by msbuild yet (tried locally).

In short, we're hitting things that @radical is trying to address in https://bugzilla.xamarin.com/show_bug.cgi?id=53164.

I'm closing this PR as he'll likely revisit switching the tests to msbuild when his fix lands.