HPCC-9419 Pass data2 through ClusterPartDiskMapSpec for overloaded

When ESP service copies a file to a roxie, the service checks slaveConfig.
If it is 'overloaded', the service calls setRoxie() which is modified to
set a new flag CPDMSF_overloadedConfig into ClusterPartDiskMapSpec. If the
flag is set, a DFUServer copies 'non-primary' file parts into predefined
defaultReplicateDir (data2, ...).

This commit also refactors a part of File Copy method in FileSpray service.
Before a DFU WU is submitted for copying a file to roxie, the existing
code sets the ClusterPartDiskMapSpec in multiple places. This commit
merges the code into one place and calls setRoxie() based on slaveConfig
setting.