Reduce the frequency in which the main loop runs

Prior to the issue_Drequest refactoring, the main loop would wait for
network connections over the wire.  Currently, it runs and sleeps for
100 microseconds before starting over.  Refactor so it does less
checking each iteration and sleep longer before starting the next
iteration.
Make sure to only print cray_enabled properties to the node file once

If the pbs_server has to rewrite the nodes file, it might write the
cray_enabled features multiple times.  It may also incorrectly put
the cray_compute property on the alps_reporter.
Merge pull request #51 from mattaezell/cray_props

Make sure to only print cray_enabled properties to the node file once
Merge pull request #13 from mattaezell/mainloop_cleanup

Reduce the frequency in which the main loop runs