Simplify/automate wwan/gsm-connection-manual description

[Pierre Equoy]

This manual job description contains the following:

2. Run `sudo network-manager.nmcli c add type gsm ifname <ifname> con-name GSM apn <your.carrier.com>` replacing the "your.carrier.com" with appropriate APN name, and ifname with appropriate interface (interface can be found by running sudo network-manager.nmcli d)

But, in Checkbox's configuration file, we have the following variables:

    $WWAN_CONTROL_IF
    $WWAN_APN

Maybe we could replace the sentence above by:

2. Run `sudo network-manager.nmcli c add type gsm ifname $WWAN_CONTROL_IF con-name GSM apn $WWAN_APN`

This way, testing it would be one copy/paste away for the QA engineers in charge of doing the manual testing ;)

[Sylvain Pineau (sylvain-pineau)]

We could also look at the duplicate bug and fix other jobs the same way.