to emulabconfig variables; this allows me to put a bunch of
passwords into a file instead of elabinelab attributes, which
land in log files, mail logs, ns files, etc.

Do not set root password to fixed string in rc.mkelab. Instead, if one
does not come in the config variables, generate a random password
string and write that into a file in /usr/testbed/etc.

Localize NAMED_VARIABLES from the config variables if it exists.