Fix wrong URLs of default security group rules management

1. 'os-security-group-rules' in the URLs should be
'os-security-group-default-rules';
2. add guide for deleting default security group rule

Change-Id: I11bf1d88182a5117da1d89696f03552c4131def6
Closes-bug: #1326950
Merge "Fix wrong URLs of default security group rules management"