libconflate doesn't handle when REST server restarts

If the REST server restarts, it appears libconflate does not notice.

In moxi (vbucket branch), there's a mock REST server that makes this easier to test...

$ ruby ./t/rest_mock.rb ./t/vbucket_rest1.cfg

control-C

$ ruby ./t/rest_mock.rb ./t/vbucket_rest2.cfg

In the 2nd restart, you'd hope to see moxi report REST config changes, but it incorrectly does not.