Fix branch releases/4.15 CI pipeline to support dotnetcore 2.1 (#6226)

* Add 'Use .NET Core sdk 2.1' to CI

* 'Use .NET Core sdk 2.1' delete installationPath

* Add 'Use .NET Core sdk 3.1'

* Revert .gitignore

* Move 'Use .NET Core sdk' tasks to all builds

* Add succeeded(), to tests tasks

build/yaml/ci-build-steps.yml

@@ -4,6 +4,18 @@ steps:
 
 # Variables ReleasePackageVersion and PreviewPackageVersion are consumed by projects in Microsoft.Bot.Builder.sln.
 # For the signed build, they should be settable at queue time. To set that up, define the variables in Azure on the Variables tab.
+- task: UseDotNet@2
+  displayName: 'Use .NET Core sdk 2.1'
+  inputs:
+    packageType: sdk
+    version: 2.1.x
+
+- task: UseDotNet@2
+  displayName: 'Use .NET Core sdk 3.1'
+  inputs:
+    packageType: sdk
+    version: 3.1.x
+
 - task: NuGetToolInstaller@1
   displayName: 'Use NuGet '
 

build/yaml/ci-test-steps.yml

@@ -32,7 +32,7 @@ steps:
      !Tests/**/Microsoft.Bot.Builder.AI.Orchestrator.Tests.csproj
      
     arguments: '-v n  -f netcoreapp2.1 --configuration release --no-build --no-restore --filter "TestCategory!=IgnoreInAutomatedBuild&TestCategory!=FunctionalTests" --collect:"Code Coverage" --settings $(Build.SourcesDirectory)\CodeCoverage.runsettings'
-  condition: and(eq(variables['BuildConfiguration'],'Release-Windows'), eq(variables['BuildTarget'],'netcoreapp21'))
+  condition: and(succeeded(), eq(variables['BuildConfiguration'],'Release-Windows'), eq(variables['BuildTarget'],'netcoreapp21'))
 
 - task: DotNetCoreCLI@2
   displayName: 'dotnet test (release) 3.1'
@@ -43,7 +43,7 @@ steps:
      !Tests/**/*21.Tests.csproj
 
     arguments: '-v n  -f netcoreapp3.1 --configuration release --no-build --no-restore --filter "TestCategory!=IgnoreInAutomatedBuild&TestCategory!=FunctionalTests" --collect:"Code Coverage" --settings $(Build.SourcesDirectory)\CodeCoverage.runsettings'
-  condition: and(eq(variables['BuildConfiguration'],'Release-Windows'), eq(variables['BuildTarget'],'netcoreapp31'))
+  condition: and(succeeded(), eq(variables['BuildConfiguration'],'Release-Windows'), eq(variables['BuildTarget'],'netcoreapp31'))
 
 - powershell: |
    # This task copies the code coverage file created by dotnet test into a well known location. In all