mkrep.sh fix for pre-existing service users.
Fixed issue where, if run more than once (or for other reasons), a replication
service user can unexpectedly exist, possibly with type 'standard' rather than
'service', before mkrep.sh is called, resulting in a failure. A sample error is:
Error in user specification.
User type can't be changed.
mkrep.sh (line: 1143): FATAL: Failed to load user spec from file: /tmp/tmp.kSIh9LeNBO/svc_p4d_ha_bos.user.p4s