* Update dependencies from https://github.com/dotnet/arcade build 20191002.6
- Microsoft.DotNet.Arcade.Sdk - 1.0.0-beta.19502.6
* Migrate to Azure Artifacts feed for tools
* Match repo-local version references to 3.0.100
* NuGet packages that get deployed into bootstrap
* the SDK itself
* Include RuntimeIdentifierGraph.json in bootstrap
Avoids errors when building with the bootstrapped build like
```
src/MSBuild/MSBuild.csproj(0,0): error NU1007: The runtime.json specified in the project '/Users/vsts/agent/2.158.0/work/1/s/stage1/bin/bootstrap/netcoreapp2.1/MSBuild/RuntimeIdentifierGraph.json' could not be found.
```
* NuGet 5.3 warnings
* Explicitly specify 4.7.2 in CoreXT package
* Use in-package icon rather than URL
* Use hosted pool
For reasons I don't fully understand, specifying the 'Hosted' pool name
caused the use of different machines, even though it seems like it's
redundantly specifying the default. Removing the specification entirely
assigns to the machines I expect.
Rainer Sigwald
Lachlan Ennis
Daniel Plaisted
Ben Villalobos
dotnet-maestro[bot]
Tomáš Matoušek
Livar
Livar Cunha
Andy Gerlicher
Jeff Kluge