External Override for per-benchmark parameters.
Changed all configure scripts to allow parameter override by defining it on the calling sub-shell before invoking (sourcing) configure.sh from within the prepare.sh and run.sh. This is done by defining a new function "setvardef" that sets a shell variable with a default value, only if said variable is still not set on the calling shell. This manner, CBTOOL (aka CloudBench) can pass parameters (e.g., DATASIZE, NUM_REDS) defined from within its interface to the actual benchmark scripts. Please note that the only changes were executed on */conf/configure.sh scripts, and the usual behavior (i.e., calling prepare.sh and run.sh) remain exactly the same, including the exactly same values as defaults for each parameter.
Bugfix on function "dir_size", allowing it to properly parse the directory size even if the HDFS contains an IP address instead of a hostname.