Change linux machine pool and remove Ubuntu 14.04

Author: nguerrera

.vsts-ci.yml

@@ -83,29 +83,12 @@ stages:
               _PublishType: none
               _SignType: test
 
-    - template: /eng/build.yml
-      parameters:
-        agentOs: Ubuntu_14_04
-        pool:
-          name: Hosted Ubuntu 1604
-        strategy:
-          matrix:
-            Build_Debug:
-              _BuildConfig: Debug
-              _PublishType: none
-              _SignType: test
-            Build_Release:
-              _BuildConfig: Release
-              _PublishType: none
-              _SignType: test
-        variables:
-          _PREVIEW_VSTS_DOCKER_IMAGE: microsoft/dotnet-buildtools-prereqs:ubuntu-14.04-cross-0cd4667-20170319080304
-
     - template: /eng/build.yml
       parameters:
         agentOs: Ubuntu_16_04
         pool:
-          name: Hosted Ubuntu 1604
+          name: NetCorePublic-Pool
+          queue: BuildPool.Ubuntu.1604.Amd64.Open
         strategy:
           matrix:
             Build_Debug:
@@ -116,8 +99,6 @@ stages:
               _BuildConfig: Release
               _PublishType: none
               _SignType: test
-        variables:
-          _PREVIEW_VSTS_DOCKER_IMAGE: microsoft/dotnet-buildtools-prereqs:ubuntu-16.04-cross-e435274-20180628134544
 
     - template: /eng/build.yml
       parameters:
@@ -165,7 +146,8 @@ stages:
       parameters:
         agentOs: Linux_Perf_CI
         pool:
-          name: Hosted Ubuntu 1604
+          name: NetCorePublic-Pool
+          queue: BuildPool.Ubuntu.1604.Amd64.Open
         strategy:
           matrix:
             Build_Release:
@@ -184,4 +166,4 @@ stages:
 - ${{ if and(ne(variables['System.TeamProject'], 'public'), notin(variables['Build.Reason'], 'PullRequest')) }}:
   - template: /eng/common/templates/post-build/post-build.yml
     parameters:
-      enableSymbolValidation: false
+      enableSymbolValidation: false