pam: Don't ask for fingerprints for remote logins

As written in the "Linux-PAM Application Developers' Guide"
at http://www.linux-pam.org/Linux-PAM-html/adg-security-user-identity.html:
"
As a general rule, the following convention for its value can be
assumed: NULL = unknown; localhost = invoked directly from the
local system; other.place.xyz = some component of the user's
connection originates from this remote/requesting host.
"

So also exit early if the hostname isn't localhost as it should be.

Closes: #21
2 jobs for wip/hadess/fix-no-ssh-pam in 3 minutes and 33 seconds (queued for 2 minutes and 5 seconds)
Status Job ID Name Coverage
  Test
passed #482474
build_dev

00:01:34

passed #482473
build_stable

00:01:59