fix #1670: change PAM service name to project specific name

fix #1670: change PAM service name to project specific name

Instead of 'common-auth' use 'proxmox-ve-auth', this way
users can override PAM authentication settings via
`/etc/pam.d/proxmox-ve-auth`.

If the file does not exist, pam will use `/etc/pam.d/other`
which by default behaves like `common-auth`.

Note that this *can* be different from directly using
`common-auth` *if* a user has actually modified
`/etc/pam.d/other` for some reason.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>