MSVC 2015 -> 2017 (#29754 An error occurred )

* MSVC 2015 -> 2017

* Update by review

BUILDING.md

@@ -55,7 +55,7 @@ installed by `brew` is being used:
 ## Windows
 
 To prepare for cmake + Microsoft Visual C++ compiler build
-- Install Visual Studio 2015 or 2017 (Visual C++ compiler will be used).
+- Install Visual Studio 2017 or later (Visual C++ compiler will be used).
 - Install [Git](https://git-scm.com/).
 - Install [CMake](https://cmake.org/download/).
 - Install [nasm](https://www.nasm.us/) and add it to `PATH` (`choco install nasm`) - *required by boringssl*

tools/run_tests/helper_scripts/build_cxx.bat

@@ -21,14 +21,6 @@ cd cmake
 mkdir build
 cd build
 
-If "%GRPC_BUILD_ACTIVATE_VS_TOOLS%" == "2015" (
-  @rem set cl.exe build environment to build with VS2015 tooling
-  @rem this is required for Ninja build to work
-  call "%VS140COMNTOOLS%..\..\VC\vcvarsall.bat" %GRPC_BUILD_VS_TOOLS_ARCHITECTURE%
-  @rem restore command echo
-  echo on
-)
-
 @rem Workaround a bug where VS150COMNTOOLS is not set due to a bug in VS 2017 installer
 @rem see https://developercommunity.visualstudio.com/t/installing-visualstudio-build-tools-doesnt-add-env/17435
 set "VS150COMNTOOLS=C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\Tools\"

tools/run_tests/run_tests.py

@@ -252,25 +252,18 @@ class CLanguage(object):
             _check_compiler(self.args.compiler, [
                 'default',
                 'cmake',
-                'cmake_ninja_vs2015',
                 'cmake_ninja_vs2017',
-                'cmake_vs2015',
                 'cmake_vs2017',
                 'cmake_vs2019',
             ])
             _check_arch(self.args.arch, ['default', 'x64', 'x86'])
 
             activate_vs_tools = ''
-            if self.args.compiler == 'cmake_ninja_vs2015' or self.args.compiler == 'cmake' or self.args.compiler == 'default':
+            if self.args.compiler == 'cmake_ninja_vs2017' or self.args.compiler == 'cmake' or self.args.compiler == 'default':
                 # cmake + ninja build is the default because it is faster and supports boringssl assembly optimizations
-                # the compiler used is exactly the same as for cmake_vs2015
-                cmake_generator = 'Ninja'
-                activate_vs_tools = '2015'
-            elif self.args.compiler == 'cmake_ninja_vs2017':
+                # the compiler used is exactly the same as for cmake_vs2017
                 cmake_generator = 'Ninja'
                 activate_vs_tools = '2017'
-            elif self.args.compiler == 'cmake_vs2015':
-                cmake_generator = 'Visual Studio 14 2015'
             elif self.args.compiler == 'cmake_vs2017':
                 cmake_generator = 'Visual Studio 15 2017'
             elif self.args.compiler == 'cmake_vs2019':
@@ -1537,9 +1530,7 @@ argp.add_argument(
         'electron1.6',
         'coreclr',
         'cmake',
-        'cmake_ninja_vs2015',
         'cmake_ninja_vs2017',
-        'cmake_vs2015',
         'cmake_vs2017',
         'cmake_vs2019',
         'mono',