HPCC-10536 Remove hardcoded references to c:\ and /c$

There are a couple places (dlslerver.cpp and rmtspawn.cpp) where a default
filespec is used when querying the environment for temp and log directories
fail. Although this is unlikely, these default locations need to be updated
to use the HPCCSystems standard locations

Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>