Merge branch 'release-v1.6.0' into master2

Changelog and version bump for PyCrypto/cryptography swap.

Fixed a bug in Cumulus Linux prompt patterns.
- Also disabled execution of `sudo vtysh` by default on Cumulus. It
  will now be left up to operators to do this for themselves.
- Updated the changelog to include a mention of the new support for
  Cumulus Linux.

Bugfix on Arista devices causing prompt to appear in command results.

Fixup of rc5 bugs (#307)
* Fixup of rc5 bugs
* TextFSM processor bug which made it so only one set of parsed commands made it into the results.
* Twister bug which regressed support for less than average ssh server implementations by not initialising keyexchange
* Made some modifications after observing a different kind of failure with the last revision. Looks like kexinit is for the server side of things.
* Applied fix to twister2 which is also affected
* Fix import bug.
* Update changelog and version control

Release 1.5.10 (#281)
Bug Fixes
---------
- Extended prompt detection for IOS-like devices to include interstitial
  space (`\s`) or carriage return (`\r`) characters which is sometimes
  seen on Arista EOS devices, and would cause asynchronous execution to
  sometimes hang and result in a `~trigger.exceptions.CommandTimeout`
  error.
- Bugfix in `bin/load_acl` that prevents `queue.complete()` from being
  called when using the `--no-db` flag.  Previously, an `AttributeError`
  attribute error was raised due to attempting to call `complete` on
  `queue`, which is set to `None` when passing `--no-db`.
- Cleaned up network.utils.ping, removed hostname validation code
- Bugfix in `~trigger.utils.network.ping()` where a file descriptor
  wasn't closed cleanly.
- Bugfix in `bin/gnng` that printed device names before any tables,
  resulting in potentially confusing results.  Devices names are now
  printed with the corresponding table.
- Bugfix in `bin/gnng` that allows the `--filter-on-type` to function as
  expected.
- Update documentation of `gnng`'s `-N`/`--nonprod` flag.
- Bugfix in `bin/gnng` that allows `gnng` to fail gracefully when a
  device isn't found.
- Bugfix in `bin/gnng --all` that was causing many device vendors to be
  skipped entirely because the filter was too specific. This vendor
  filter has been removed and will now fallback to
  `~trigger.cmds.NetACLInfo()` internal knowledge of supported
  platforms.

Release 1.5.9
Bug Fixes
---------
+ Bugfix in `~trigger.gorc` where init commands would be sent
  before a prompt was even available on the remote device.
+ Bugfix in `~trigger.utils.core.pretty_time()` where `pytz` was
  being referenced but not imported.
+ Extended prompt detection for IOS-like devices to include backspace
  characters (`\b` or `\x08`) which is sometimes seen on Cisco NX-OS
  devices, and would cause asynchronous execution to sometimes hang and
  result in a `~trigger.exceptions.CommandTimeout` error.
* Improved the internal grouping logic for `load_acl` to be more
  permissive and if grouping fails it will just not group devices.
* Fixed a bug that would prevent ACL staging from working when using
  default global settings.
* Fixed bugs in the default global callables for `get_current_oncall()`
  and `create_tm_ticket()` that would prevent `lod_acl` from working.
  They now default to a disabled state that does not require
  customization just to utilize core load_acl functionality.
* Updated the sample `settings.py` (`conf/trigger_settings.py`) to
  utilize the updated default callables.
* Fixed a bug in default global callable for `get_tftp_source()` to
  properly perform lookup of `settings.VIPS`
* Fixed a bug in default global callable for `stage_acls()` to
  properly perform lookup of `settings.FIREWALL_DIR` and
  `settings.TFTPROOT_DIR`.

Release 1.5.8
Bug Fixes
---------
+ Bugfix in `~trigger.cmds.Commando` related to the addition of TextFSM
  support for parsing unstructured CLI output.

Release 1.5.7
Enhancements
------------
- Added TextFSM parser to process unstructured CLI output.
- Added a new prompt pattern to `settings.CONTINUE_PROMPTS`.
- New continue prompts no longer need to be lower-cased.
- Clarified the error text when an enable password is required but not
  provided when connecting to a device to make it a little more clear on
  how to proceed.
Bug Fixes
---------
- Bugfix in `~trigger.contrib.commando.plugins.config_device` causing an
  unhandled `NameError`.
- Bugfix in `bin/gnng` that would cause a crash when using
  `--sqldb` or `--csv` output flags.

Release 1.5.6
Bug Fixes
---------
* Added `-f/--force-cli` to `run_cmds` to allow CLI execution
  on Juniper devices or any vendor platform where API support is enabled
  by default, fixing an underlying bug where CLI output would result in a
  crash.
* Multiple commands can now be sent to Juniper devices w/ `run_cmds`.
* Updated the Juniper CLI prompt pattern to work when a hostname isn't set
  that would result in a `CommandTimeout` causing execution to fail.