[source] Fix and improve metrics submission test
[source] Fix and improve metrics submission test

- Fix the test always succeeding
- Enable error trap in metrics submission test
- Print dots of test progression in console output
- Allow the test to run with either `curl` or `wget`
- Small changes in output messages (`agent` --> `Agent`, grammar)

Wattpad/dd-agent,takus/dd-agent,pmav99/praktoras,jyogi/purvar-agent,pmav99/praktoras,Wattpad/dd-agent,pmav99/praktoras,indeedops/dd-agent,takus/dd-agent,indeedops/dd-agent,lookout/dd-agent,jyogi/purvar-agent,takus/dd-agent,gphat/dd-agent,pmav99/praktoras,lookout/dd-agent,cberry777/dd-agent,cberry777/dd-agent,brettlangdon/dd-agent,indeedops/dd-agent,c960657/dd-agent,jyogi/purvar-agent,c960657/dd-agent,jyogi/purvar-agent,tebriel/dd-agent,gphat/dd-agent,brettlangdon/dd-agent,Wattpad/dd-agent,cberry777/dd-agent,tebriel/dd-agent,brettlangdon/dd-agent,manolama/dd-agent,takus/dd-agent,tebriel/dd-agent,gphat/dd-agent,brettlangdon/dd-agent,gphat/dd-agent,lookout/dd-agent,brettlangdon/dd-agent,pmav99/praktoras,manolama/dd-agent,takus/dd-agent,manolama/dd-agent,lookout/dd-agent,tebriel/dd-agent,indeedops/dd-agent,manolama/dd-agent,lookout/dd-agent,gphat/dd-agent,manolama/dd-agent,c960657/dd-agent,c960657/dd-agent,jyogi/purvar-agent,cberry777/dd-agent,c960657/dd-agent,Wattpad/dd-agent,indeedops/dd-agent,cberry777/dd-agent,tebriel/dd-agent,Wattpad/dd-agent