Improve error message when arguments missing for vnf-events-list command

[vishwanath jayaraman]

Executing the command "tacker vnf-events-list <vnf_id>" displays the below error message that fails to convey what arguments are missing.

Invalid values_specs <vnf_id>

The correct command should have been "tacker vnf-events-list --resource_id <vnf_id>".
The error message should have thrown meaningful message that would have listed the usage and supported arguments such as below:

usage: tacker vnf-events-list [-h] [-f {csv,html,json,table,value,yaml}]
                              [-c COLUMN] [--max-width <integer>] [--noindent]
                              [--quote {all,minimal,none,nonnumeric}]
                              [--request-format {json,xml}] [-D] [-F FIELD]

List events that belong to a given VNF. The supported args are --id,
--resource_id, --resource_state, --event_type

[Sridhar Ramaswamy (srics-r)]

Unassigned due to inactivity, pike candidate

[dharmendra (dharmendra-kushwaha)]

Fixed in https://review.opendev.org/#/c/667528/