Gong now enables on login if the enable password is provided

fix #142

- send_enable() and requires_enable() moved to top-level helper
  functions within trigger.twister
- All commands now sent with CRLF (\r\n) instead of just LF (\n)
  due to compatibility with certain vendor platforms
- Newlines have been removed startup_commands for NetDevice
  objects and are now instead sent by the SSH client factory
  like other commands
- Adjusted the prompt matching pattern for F5 that was causing
  it not to match in certain cases