Use boost::filesystem for looking in /proc
Use boost::filesystem for looking in /proc

This simplifies the code and error handling

Change-Id: I6c1c8d611af6b66311f7dc7ac64ffbfba9915824
Reviewed-on: https://review.couchbase.org/c/sigar/+/169806
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

couchbase/sigar,couchbase/sigar