Add force option if the users do not exist in the machine (needed for e.g. EUDAT B2STAGE)

[RubenGarcia]

When using gtc and EUDAT B2STAGE, the users may not be connected to the unix users in the machine (e.g. if authorization uses OpenID tokens).
I added an option to allow modification of the gridmap file even if the unix user does not exist (-f -- force)

[fscheiner]

@matyasselmeci
Strange, the Travis-CI check didn't work or didn't finish since Aug 18th, 3:00 PM GMT+2. I also don't see it on Travis-CI. Can this check be retriggered somehow?

[fscheiner]

@RubenGarcia
Could you please make the change to https://github.com/gridcf/gct/pull/134/files#diff-970a287b14b8f63d7c4d1b1660881053, recreate the corresponding manpage and force-push your changes, so the PR gets updated?

I'd do it myself, but the GUI seems to not allow changes to your branch from me. Maybe because you create the PR from your master branch and not a "feature" branch.

[fscheiner]

@RubenGarcia
It could also be due to that you unchecked the "Allow edits by maintainers" checkbox when creating this PR, that I am unable to update your changes. I think allowing such changes in future PRs could speed up their inclusion, so better keep this checkbox always checked.

[RubenGarcia]

I can't find how to change the option, so I'll perform your changes.

[fscheiner]

I can't find how to change the option, so I'll perform your changes.

Indeed, I think this can only be activated when creating the PR.

[fscheiner]

Looks good to me.