title: SerilogFactory don't log my messages but it logs exceptions
body: <p>I want to use the SerilogFactory, the LogFactory is initialized before initializing the AppHost.
  This is my startup.cs :</p>
  
  <pre><code>public class Startup
  {
      public Startup(IConfiguration configuration)
      {
          Configuration = configuration;
      }
  
      public IConfiguration Configuration { get; }
  
      public void ConfigureServices(IServiceCollection services)
      {
      }
  
      public void Configure(IApplicationBuilder app, IHostingEnvironment env)
      {
          if (env.IsDevelopment())
          {
              app.UseDeveloperExceptionPage();
          }
  
          var logger = new LoggerConfiguration().WriteTo.File("log.txt").CreateLogger();
          LogManager.LogFactory = new SerilogFactory(logger);
  
          app.Map("/api", api =&gt;
          {
              api.UseServiceStack(new AppHost(env.ApplicationName, Configuration));
          });
     }
  }
  </code></pre>
  
  <p>And this is my sample service :</p>
  
  <pre><code>public class TestService : ServiceStack.Service
  {
      public static ILog Log = LogManager.GetLogger(typeof(TestService));
  
      public bool Get(GetTest request)
      {
          Log.Info("foo");
          Log.Warn("???");
  
          throw new System.Exception("plop");
  
          return true;
      }
  }
  </code></pre>
  
  <p>After calling the "GetTest" request, I can see the details of the exception in my "log.txt" file but I can't see the Info "foo" or the Warm "???" in the file.</p>
  
  <pre><code>2019-07-03 18:07:55.597 +02:00 [INF] Initializing Application Tmpi.PocketTournee took 352.2006ms. No errors detected.
  2019-07-03 18:08:07.446 +02:00 [ERR] ServiceBase&lt;TRequest&gt;::Service Exception
  System.Exception: plop
  at Tmpi.PocketTournee.ServiceInterface.TestService.Get(GetTest request) in C:\Projects\VS2017\PocketTournee\WebService\Sources\Tmpi.PocketTournee.ServiceInterface\TestService.cs:line 15
  </code></pre>
  
  <p>If I initialize the LogFactory AFTER initializing the AppHost, I can see my own logs but this time the exception details and the servicestack init info have disappeared :</p>
  
  <pre><code>2019-07-03 18:25:05.420 +02:00 [INF] foo
  2019-07-03 18:25:05.434 +02:00 [WRN] ???
  </code></pre>