Fix bin/load_acl to check .tacacsrc before work begins

- Perform this check before the curses board is drawn
- Also, log this and exit cleanly under load_acl --auto
Fixing skip phrasing for next maintance window in bin/load_acl
Improvements to user-experience within bin/acl

- It now requires users to explicitly ask for associations
  instead of it being default.
- The wording on the status output has been improved for clarity
  and conciseness.
Gong now uses chosen dev. from multiple when updating .tacacsrc

fix #151
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
Fix bugs in auto-enable and remote execution on certain devices

- The correct delimiter is now mapped out by vendor/platform and
  attached to the NetDevice object at runtime.
- Fixed a bug when executing commands remotely on NetScreen
  devices running ScreenOS that was causing them to be treated
  as Juniper routers/switches if the NetDevice attributes
  vendor=juniper and deviceType=netscreen.