sched: update rexec.run event

The name of the event that wrexec subscribes to changed from rexec.run
to wrexec.run.  This commit changes the sched code to match.
sched: modify lua require statements in flux-submit

This incorporates the same changes made to flux-wreckrun to detect
LUA_PATH problems
Merge pull request #5 from lipari/flux-submit_fix

Fixes for flux-submit and wrexec.run event