Issue #2060 - cinnamon-settings can hang

If any subprocesses executed by cs_info.py hang (such as a hung
NFS mount preventing "df" from returning), then cinnamon-settings
will never start.

This adds a 2 second timeout for any subprocess which will cancel
the operation and kill the process if all output isn't received
during the timeout period.
Merge pull request #2082 from scotte/2060_cinnamon-settings_hang

Issue #2060 - cinnamon-settings can hang