Get bosh_cli to work with Director on https with port 443

Fix for https://github.com/cloudfoundry/bosh/issues/557
Thanks for finding the cause of this problem. The main issue with the PR is that it is missing tests. We should test that `normalize_url ` method is idempotent. 

```
original_uri = 'https://localhost'
first_url = base_command.normalize_url(original_uri)
expect(first_url).to eq('https://localhost:25555')
second_url = base_command.normalize_url(first_url)
expect(second_url).to eq(first_url)
```

Other suggestions would be:

1. We should strip trailing slash at the beginning since `had_port` is looking for the port at the end of URL without slash.
2. We can be consistent with the port matching and just set the default port if it is missing instead of introducing `uri_to_string` method which is not easy to follow. We can still use URI.parse for validation.

```
def normalize_url(url)
  URI.parse(url)

  url.gsub!(/\/$/, '')
  url = "https://#{url}" unless url =~ /^http:?/

  unless url.to_s =~ /:\d+$/
    url += ":#{DEFAULT_DIRECTOR_PORT}"
  end

  url
end
```