not copy nuget package to build output to save disk space

[frank-dong-ms-zz]

dotnet core 3.0 build use too much disk space (more than 16GB) and cause build failure on CI, this is caused by below line of code from build tools (\Tools\dotnetcli\sdk\3.0.100\Sdks\Microsoft.NET.Sdk\targets\Microsoft.PackageDependencyResolution.targets):

<CopyLocalLockFileAssemblies Condition="'$(CopyLocalLockFileAssemblies)' == '' and
                                        '$(TargetFrameworkIdentifier)' == '.NETStandard'">false</CopyLocalLockFileAssemblies>

<!-- Don't copy local for netcoreapp projects before 3.0 or non-exe and non-component projects. -->
<CopyLocalLockFileAssemblies Condition="'$(CopyLocalLockFileAssemblies)' == '' and
                                        '$(TargetFrameworkIdentifier)' == '.NETCoreApp' and
                                        ('$(_TargetFrameworkVersionWithoutV)' &lt; '3.0' or
                                         ('$(HasRuntimeOutput)' != 'true' and '$(EnableDynamicLoading)' != 'true'))">false</CopyLocalLockFileAssemblies>

<!-- All other project types should copy local. -->
<CopyLocalLockFileAssemblies Condition="'$(CopyLocalLockFileAssemblies)' == ''">true</CopyLocalLockFileAssemblies>

Override CopyLocalLockFileAssemblies setting to false to save disk space.

Also, change windows netcore 3.0 build to use hosted test agent.