Exit on installer failure

[tahg]

In the case ServerStarter runs into issues while startup up, it should exit. On Windows, adding pause would help as well. On Linux it's less likely to be necessary, as having a console that closes when finished is rarer.

In my case, the installer failed to delete a directory because I accidently had a file open, but there any error during install could cause problems. As it stands, ServerStarter will continue to actually start the server even if there was an error, which can lead to missing mods or config, or world corruption.