Tweaked HMS mkrep.sh script to avoid using p4login, as p4login assumes
it is being run on a server where there the given SDP instance is configured.
Normally the way p4login is used, that's a safe assumption. But in this case
mkrep.sh is intended to be called on the HMS server, which may not actually
host the SDP instance for which a replica is being made. They will have their
p4_N.vars files in /p4/common/config, but may not have a /p4/N/root or even
/p4/N directory on the HMS server itself.
This introduces a dependency, deemed acceptable for HMS purposes, that all
instances that use this mkrep.sh script have the same password for the
'perforce' super user as the hms instance, as it uses only the
/p4/common/config/.p4passwd.p4_hms.admin password file (for the /p4/hms