AutobahnTester should use dynamic port "0" with Kestrel

[mikeharder]

Changes should be made to AutobahnTester and/or SelfHostDeployer to use dynamic port "0" for ServerType.Kestrel. Currently, it uses the less-reliable GetNextPort() method.

This is somewhat complicated since AutobahnTester requires HTTPS, which is currently only supported in SelfHostDeployer when DeploymentParameters.ApplicationBaseUriHint is set, but dynamic port "0" is only used when ApplicationBaseUriHint is not set. So, there are two options (in my order of preference):

1. Add an Ssl parameter to DeploymentParameters, then change AutobahnTester to set DeploymentParameters.Ssl instead of DeploymentParameters.ApplicationBaseUriHint. This will use dynamic port "0" for ServerType.Kestrel (both HTTP and HTTPS), and GetNextPort() for ServerType.WebListener (since dynamic port "0" is not supported).

2. Change SelfHostDeployer to use dynamic port "0" when ApplicationBaseUriHint is set to either "127.0.0.1:0" or "[::1]:0". Dynamic port "0" is not supported on other hostnames which try to bind both IPv4 and IPv6, like "localhost". Then change AutobahnTester to use "http[s]://127.0.0.1:0" instead of "http[s]://localhost:0".

https://github.com/aspnet/WebSockets/blob/612db427725b3bdac3d6851288c93051bfe69621/test/Microsoft.AspNetCore.WebSockets.ConformanceTest/Autobahn/AutobahnTester.cs#L132

Related: aspnet/Hosting#1296