[BUG][CSHARP][GENERICHOST] Write enum values in expected JSON format #212

Job	Run time
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/FormModels)	1m 55s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/Petstore)	1m 24s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AllOf)	2m 3s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOfNoCompare)	1m 27s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/UseDateTimeForDate)	1m 4s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/AnyOf)	1m 8s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.7/OneOf)	1m 42s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AllOf)	1m 33s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/OneOf)	1m 25s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOfNoCompare)	2m 14s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/Petstore)	1m 24s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/AnyOf)	1m 5s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/FormModels)	1m 39s
Build .Net projects (samples/client/petstore/csharp/generichost/net4.8/UseDateTimeForDate)	1m 5s
	21m 8s

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