Avoid regex in GetVsRootFromMSBuildAssembly
Avoid regex in GetVsRootFromMSBuildAssembly

Also eliminates the unspecified need to only pass in MSBuild.exe as the
assembly.

AndyGerlicher/msbuild,AndyGerlicher/msbuild,AndyGerlicher/msbuild,rainersigwald/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild