refactor error-checking result

[wibeasley]

There are several functions with code like this. Pull it out into a reusable & testable function

  regex_cannot_connect <- "^The hostname \\((.+)\\) / username \\((.+)\\) / password \\((.+)\\) combination could not connect.+"
  regex_empty <- "^\\s+$"

  if(
    any(grepl(regex_cannot_connect, raw_text)) |
    any(grepl(regex_empty, raw_text))
  ) {
    success <- FALSE
  }

Stepping back more, I now see how more could be included, starting with the httr::POST() call too. Someone (I think @nutterb) has been advocating this for at least year --I'm just now catching up.