Fixed issue with detection of whether 'perforce' user pre-exists if it
was created with LDAP (where the 'id -u' is not a reliable check). This
resulted in a failure to create the perforce OS user because 'useradd'
won't work in an LDAP environment.
Warning: Review code carefully; the test suite does not currently simulate
an LDAP environment, so this requires manual testing in an LDAP environemt,
at least for now.