MMS Read environment variables only

For ease of shared development each user wanting to run MMS should set up environment variables with the following names:
CAL_PATH_ROOT  - to Calib files
CDF_BASE       - to CDF executables (not currently used)
DATA_PATH_ROOT - to the CDF data files (file structure as described in MMS_SDC_DEVELOPER_GUIDE)
DROPBOX_ROOT   - to where the output files should be placed (must be writeable by user).
LOG_PATH_ROOT  - to where the logs should end up