condor_sysapi: Add detection of Rocky Linux 8.
condor_sysapi: Add detection of Rocky Linux 8.

This fixes detection so x64/Rocky8 is shown instead of x64/LINUX0,
in terms of classads:
 OpSys = "LINUX"
 OpSysAndVer = "Rocky8"
 OpSysLegacy = "LINUX"
 OpSysLongName = "Rocky Linux release 8.4 (Green Obsidian)"
 OpSysMajorVer = 8
 OpSysName = "Rocky"
 OpSysShortName = "Rocky"
 OpSysVer = 804

Signed-off-by: Oliver Freyermuth <297815a44ac0d229e08a814adf0f210787d04d87@googlemail.com>

htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor