Improve NGINX start

[pleshakov]

Proposed changes

Improve how the IC starts NGINX

For NGINX and NGINX Plus:

• After the IC starts NGINX, check that NGINX is running by
  querying the config version via the unix socket -- the same check
  that is performed after each configuration reload.
• Modify the check to always sleep before the first check.

For NGINX Plus:

• Remove no longer required 0.5s timeout during the IC start.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto master
• I will ensure my PR is targeting the master branch and pulling from my branch from my own fork

[isaachawley]

👍