Expand PAM data support in the fakepam library

Add full support for PAM_RHOST, PAM_RUSER, and PAM_TTY and read-only
support for PAM_SERVICE (returning the service name given to
pam_start) and PAM_USER_PROMPT (returning "login: ") to the fake PAM
library for testing.

Also use calloc in one place instead of initializing pointers.
Add optional PKINIT configuration to kerberos_setup test function

In the TAP add-on for Kerberos testing, add a new flag,
TAP_KRB_NEEDS_PKINIT, to the kerberos_setup function.  This indicates
that configuration for PKINIT authentications is required for this
test case.
Fix error message for missing pam-util/options-t.c test data