Merge pull request #1263 from jtattermusch/use_openssl_nuget

src/csharp/Grpc.Core/Grpc.Core.csproj

src/csharp/Grpc.Core/packages.config

templates/vsprojects/Grpc.mak.template

templates/vsprojects/gpr/gpr.vcxproj.filters.template

templates/vsprojects/gpr/gpr.vcxproj.template

...s/vsprojects/gpr_test_util/gpr_test_util.vcxproj.template

templates/vsprojects/grpc++/grpc++.vcxproj.filters.template

templates/vsprojects/grpc++/grpc++.vcxproj.template

templates/vsprojects/grpc.sln.template

templates/vsprojects/grpc/grpc.vcxproj.filters.template

templates/vsprojects/grpc/grpc.vcxproj.template

templates/vsprojects/grpc/packages.config.template

...projects/grpc_csharp_ext/grpc_csharp_ext.vcxproj.template

...lates/vsprojects/grpc_csharp_ext/packages.config.template

...vsprojects/grpc_test_util/grpc_test_util.vcxproj.template

...ects/grpc_unsecure/grpc_unsecure.vcxproj.filters.template

...s/vsprojects/grpc_unsecure/grpc_unsecure.vcxproj.template

templates/vsprojects/grpc_unsecure/packages.config.template

templates/vsprojects/packages.include

templates/vsprojects/vcxproj.filters_defs.include