Simplify code by keeping memory/disk in megabytes.

Memory was kept in kilobytes, and disk in megabytes, but as a double.
Read cores/memory/disk resources from environment.

The environment variable CORES, MEMORY, and DISK, are read from the
environment and set for the default resource category in Makeflow.
Monitor reads memory/disk/cores limits from env.
Makeflow reads cores/disk/resources from file.