IPMI sensor plugin times out

[m4ce]

We should be able to specify a timeout for the ipmi_sensor input plugin.

2017-05-16T12:55:05Z E! Error in plugin [inputs.ipmi_sensor]: failed to run command /usr/bin/ipmitool sdr: Command timed out. -

[danielnelson]

Turns out this is a duplicate of #1565.