support empty password

[jsvd]

fixes #614

[jsvd]

these test failures are very strange, it seems only the tests are being used, not the library code

[webmat]

The CGI.unescape exceptions happen in another code path: the healthcheck code path. In it, manticore_adapter.rb does try to read back the password from the ::LogStash::Util::SafeURI instance (which in turn returns nil when empty).

If we guard for a nil password here as well (e.g. with CGI.unescape(url.password || '')) then the we get 1/2 tests passing. The one with the empty password in the options.

The other one still reads a nil password from the hosts URI instances, and password is not forced to '' when nil.

I wonder if just adding the aforementioned || '' in manticore_adapter.rb would actually be enough to support empty passwords.