Fix ASP.NET

Plaintext, JSON and database tests should all work except for the fortunes tests.

Had to downgrade to ASP.NET MVC 4. When mono is released with [these changes](https://github.com/mono/mono/pull/1163), we can upgrade to ASP.NET MVC 5.2.2 and the fortunes tests will also work.

When I launch nginx myself, everything seems to work. But `toolset/run-tests.py --mode verify --install server --test aspnet-mono` doesn't work for some reason.

```
vagrant@TFB-all:~/FrameworkBenchmarks$ cat results/ec2/latest/logs/aspnet-mono/out.txt
test.os.lower() = linux  test.database_os.lower() = linux
self.results['frameworks'] != None: True
test.name: aspnet-mono
self.results['completed']: {u'aspnet-mono': u'port 8080 is not available before start'}
```
No, the first couple of lines from https://github.com/TechEmpower/FrameworkBenchmarks/blob/master/toolset/setup/linux/languages/mono.sh checks to see if `mono.installed` exists and returns without setting the envvars if it does.