* Refactor common network shared and platform specific code into package (part-1)
As per proposal #76 refactor common network shared and platform specific
code into sub-package.
https://github.com/ansible/proposals/issues/76
* ansible.module_utils.network.common - command shared functions
* ansible.module_utils.network.{{ platform }} - where platform is platform specific shared functions
* Fix review comments
* Fix review comments
* Add junos_banner declartive module
* junos_banner implementation
* Integration test for junos_banner
* Integration test for net_banner (junos)
* Minor fixes
* Minor doc change
If the banner is not set, the stdout of 'show configuration | begin banner <banner>'
returns empty string thus the re.search raises an exception.
Fixes#22216