Add dot net core 2.0 support
1) add dotnet core 2.0 projects for sdk, sample and test folder.
And aliyun-oss-sdk-dotnetcore.sln has the dot net core 2.0 projects only.
while aliyun-oss-sdk.sln has all projects.
2) Fix the test cases for dotnet core 2.0.
To work with dotnet core 2.0, the supported NUnit framework is NUnit 3.9 and it replaced the attributes TestFixtureTearDown and TestFixtureTearSetup with OnetimeTearDown and OnetimeSetup.
3) Fix resource for dotnet core 2.0
Due to a dotnet core's bug (https://github.com/dotnet/coreclr/issues/12262, https://github.com/Microsoft/msbuild/issues/2221) in Linux, the MimeData could not load the content of the text file correctly. So to workaround this bug, just put the content in the resource file instead.
4) other code fixes
4.1) KeyedHashAlgorithm.Create("SHA1")) does not work anymore in dotnet core 2.0. So create the HMACSHA1 instance directly.
4.2) In sdk/Common/Communication/ServiceClientImpl.cs, always use mono way to call the reflection code when it's dotnet core 2.0
Add dot net core 2.0 support 1) add dotnet core 2.0 projects for sdk, sample and test folder. And aliyun-oss-sdk-dotnetcore.sln has the dot net core 2.0 projects only. while aliyun-oss-sdk.sln has all projects. 2) Fix the test cases for dotnet core 2.0. To work with dotnet core 2.0, the supported NUnit framework is NUnit 3.9 and it replaced the attributes TestFixtureTearDown and TestFixtureTearSetup with OnetimeTearDown and OnetimeSetup. 3) Fix resource for dotnet core 2.0 Due to a dotnet core's bug (https://github.com/dotnet/coreclr/issues/12262, https://github.com/Microsoft/msbuild/issues/2221) in Linux, the MimeData could not load the content of the text file correctly. So to workaround this bug, just put the content in the resource file instead. 4) other code fixes 4.1) KeyedHashAlgorithm.Create("SHA1")) does not work anymore in dotnet core 2.0. So create the HMACSHA1 instance directly. 4.2) In sdk/Common/Communication/ServiceClientImpl.cs, always use mono way to call the reflection code when it's dotnet core 2.0