Set the execute bit on sysDescr_pass.py (#306)

#### Why I did it
Slim images may have a sysDescr_pass.py script that does not correctly have the execute bit set resulting in any request for the sysDescr.0 OID via SNMP would fail.  By setting the execute bit directly in source control, this script is no longer reliant on any deployment script to fix the permissions after the fact.

#### How I did it
Set the execute bit directly within source control

#### How to verify it
Testing on a platform which uses a slim image should reliably pass the snmp/test_snmp_v2mib.py test.