Log exact error during getting value from file
Log exact error during getting value from file

Before this patch function get_value_from_file() was only
logging something like "Unable to access {filename}" but it
would be useful sometimes to check what was exact reason of
IOError so lets log this info also.

TrivialFix

Related-bug: #1853652

Change-Id: I28b1753a8d5767babbb6f06a581ffe1fc4ad75d3

openstack/neutron,mahak/neutron,mahak/neutron,openstack/neutron,mahak/neutron,openstack/neutron