new module exos_config (#43902)

- support config operations for EXOS-based platforms
- add regex to detect command failure responses
- add exos action plugin for "backup" operation
- add unit tests for exos_command (currently 94% coverage of
  exos_config.py)

lib/ansible/modules/network/exos/exos_command.py

@@ -37,7 +37,7 @@ description:
     module to wait for a specific condition before returning or timing out if
     the condition is not met.
   - This module does not support running configuration commands.
-    We expect to release an exos_config module soon to configure EXOS devices.
+    Please use M(exos_config) to configure EXOS devices.
 notes:
   - If a command sent to the device requires answering a prompt, it is possible
     to pass a dict containing I(command), I(answer) and I(prompt). See examples.