playbook support for vlan trunk ranges (#149)

* Provide playbook support for vlan trunk ranges in the SONiC l2_interfaces resource module:

- Change the argspec to use a string instead of an integer when specifying a vlan or
a vlan range.
- Add handling to support a "vlan" argument that specifies a vlan range in the form "X-Y".
- provide correct tracking of commands sent to the device after eliminating requested
configuration that is already present on the device.
- Fix bugs causing incorrect reporting of the original playbook command "invocation" and
the final set of commands sent to the device.
- Add regression test cases to cover the possible overlap conditions between trunk vlans
and ranges configured on the device and requested additions or deletions of trunk vlans
and ranges.

* Fix Ansible sanity errors for automatic string format field numbering.

* Fix remaining sanity errors.

* Updated the description of the trunk "vlan" argument to incorporate a vlan range

* Modified trunk vlan argument descriptions, added vlan trunk range examples

* Fix "trailing whitespace" sanity errors.

plugins/module_utils/network/sonic/argspec/l2_interfaces/l2_interfaces.py

@@ -53,7 +53,7 @@ def __init__(self, **kwargs):
                         'allowed_vlans': {
                             'elements': 'dict',
                             'options': {
-                                'vlan': {'type': 'int'}
+                                'vlan': {'type': 'str'}
                             },
                             'type': 'list'
                         }