MEDIUM: spoe-agent: properly postresolve log rings

MEDIUM: spoe-agent: properly postresolve log rings

Now that we have sink_postresolve_logsrvs() function, we make use of it
for spoe-agent log postparsing logic.

This will allow this kind of config to work:
  |spoe-agent test
  |        log tcp@127.0.0.1:514 local0
  |        use-backend xxx

Plus, consistency checks will also be performed as for regular log
directives used from global, log-forward or proxy sections.