validate NSX configuration parameters on Settings tab
validate NSX configuration parameters on Settings tab

- right now it is possible to start deploy with empty NSX settings, we
  must validate settings before deployment starts
- validate NSX username, must be not empty
- validate NSX password, must be not empty
- validate transport zone and L3 gateway UUIDs
- validate NSX endpoints and URL, must be valid IPv4 and valid
  HTTP/HTTPS URL
- while here explicitly specify in comments and warnings that right now
  we support only IPv4 addresses

Change-Id: Ie0ad618122034caf6e4a9433bf76c033e241f369
Closes-bug: #1347682

stackforge/fuel-web,koder-ua/nailgun-fcert,prmtl/fuel-web,nebril/fuel-web,SmartInfrastructures/fuel-web-dev,prmtl/fuel-web,huntxu/fuel-web,zhaochao/fuel-web,SmartInfrastructures/fuel-web-dev,eayunstack/fuel-web,nebril/fuel-web,huntxu/fuel-web,prmtl/fuel-web,koder-ua/nailgun-fcert,SmartInfrastructures/fuel-web-dev,nebril/fuel-web,nebril/fuel-web,eayunstack/fuel-web,zhaochao/fuel-web,eayunstack/fuel-web,stackforge/fuel-web,zhaochao/fuel-web,eayunstack/fuel-web,koder-ua/nailgun-fcert,huntxu/fuel-web,koder-ua/nailgun-fcert,eayunstack/fuel-web,zhaochao/fuel-web,huntxu/fuel-web,SmartInfrastructures/fuel-web-dev,stackforge/fuel-web,SmartInfrastructures/fuel-web-dev,nebril/fuel-web,prmtl/fuel-web,prmtl/fuel-web,zhaochao/fuel-web,huntxu/fuel-web