Insteon: Attempt to Reconnect PLM if it Appears to be Down

- Add flag to track if a message sent to the PLM has been acknowledged by the PLM
- On retry, if no receipt was acknowledged by the PLM, attempt to re-open the PLM serial port

Should fix hollie/misterhouse#397
Add Serial_Port_Close Routine; Insteon Close Serial Port Before Restarting

Add simple routine to mh "binary" that closes the serial port in the manner recommended by the Device::Serial_Port documentation.

Change Insteon_PLM serial port restart routine to close the port before re-creating it
Merge pull request #401 from krkeegan/fix_issue_397

Insteon: Attempt to Reconnect PLM if it Appears to be Down