Add a skip condition to all tests slower than 100ms.
This change was made using `gotestsum tool slowest` with data from the
last 3 CI runs of master.
See https://github.com/gotestyourself/gotestsum#finding-and-skipping-slow-tests
With this change:
```
$ time go test -count=1 -short ./agent
ok github.com/hashicorp/consul/agent 0.743s
real 0m4.791s
$ time go test -count=1 -short ./agent/consul
ok github.com/hashicorp/consul/agent/consul 4.229s
real 0m8.769s
```
The embedded HTTPServer struct is not used by the large HTTPServer
struct. It is used by tests and the agent. This change is a small first
step in the process of removing that field.
The eventual goal is to reduce the scope of HTTPServer making it easier
to test, and split into separate packages.
This way we can avoid unnecessary panics which cause other tests not to run.
This doesn't remove all the possibilities for panics causing other tests not to run, it just fixes the TestAgent
The default http.Client uses infinite timeouts, so if TestHTTPAPI_MethodNotAllowed_OSS experienced anything going wrong about setup it could hang forever.
Switching to hard coding various http.Client timeouts to non-infinite values at least bounds the failure time.
