HPCC-11283 Use cluster ldap user when building queries using file cache

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge pull request #5796 from afishbeck/roxieLdapUser

HPCC-11283 Use cluster ldap user when building queries using file cache

Reviewed-By: Gavin Halliday <gavin.halliday@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>