Merge pull request dotnet#37287 from dotnet/add-ubuntu-1904

Add Ubuntu 19.04 to official runs

Author: MattGal

eng/pipelines/linux.yml

@@ -115,7 +115,7 @@ jobs:
           - alpineQueues: \(Alpine.38.Amd64\)ubuntu.1604.amd64.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.8-helix-45b1fa2-20190327215821
 
         - ${{ if eq(parameters.isOfficialBuild, 'true') }}:
-          - linuxDefaultQueues: Centos.7.Amd64+RedHat.7.Amd64+Debian.8.Amd64+Debian.9.Amd64+Ubuntu.1604.Amd64+Ubuntu.1804.Amd64+Ubuntu.1810.Amd64+OpenSuse.42.Amd64+SLES.12.Amd64+SLES.15.Amd64+\(Fedora.28.Amd64\)ubuntu.1604.amd64@mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-28-helix-45b1fa2-20190402012449+\(Fedora.29.Amd64\)ubuntu.1604.amd64@mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-29-helix-c6dc5e6-20190402012449
+          - linuxDefaultQueues: Centos.7.Amd64+RedHat.7.Amd64+Debian.8.Amd64+Debian.9.Amd64+Ubuntu.1604.Amd64+Ubuntu.1804.Amd64+Ubuntu.1810.Amd64+OpenSuse.42.Amd64+SLES.12.Amd64+SLES.15.Amd64+\(Fedora.28.Amd64\)ubuntu.1604.amd64@mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-28-helix-45b1fa2-20190402012449+\(Fedora.29.Amd64\)ubuntu.1604.amd64@mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-29-helix-c6dc5e6-20190402012449+\(Ubuntu.1904.Amd64\)ubuntu.1604.amd64@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-19.04-helix-amd64-337cf5e-20190429231235
           - linuxArm64Queues: \(Ubuntu.1604.Arm64\)Ubuntu.1604.Arm64.Docker@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-16.04-helix-arm64v8-b049512-20190321153539
           - linuxArmQueues: \(Debian.9.Arm32\)Ubuntu.1604.Arm32@mcr.microsoft.com/dotnet-buildtools/prereqs:debian-9-helix-arm32v7-b049512-20190321153542
           - alpineQueues: \(Alpine.38.Amd64\)ubuntu.1604.amd64@mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.8-helix-45b1fa2-20190327215821+\(Alpine.39.Amd64\)ubuntu.1604.amd64@mcr.microsoft.com/dotnet-buildtools/prereqs:alpine-3.9-helix-e4eaef4-20190228230637