Add enable_security_group to BigSwitch and OneConvergence ini files

It is a follow up patch for https://review.openstack.org/#/c/67281/.

Change-Id: I38463b3879ab2d7469a85ef00426b2b602fa825a
Closes-Bug: #1296000
Replace a usage of the deprecated root_helper option

This change replaces a usage of the deprecated root_helper option
by the usage of get_root_helper result.

Change-Id: Icfc698243784557cbf987a817c13d0b80969e5d3
Closes-Bug: #1297145
ML2 Cisco Nexus MD: Remove workaround for bug 1276395

Before bug 1276395 was merged the delete_port_postcommit() mechanism
drivers did not have access to the bound_segment information that was
in the process of being deleted.
Code was added to the cisco_nexus md to workaround this issue.
This code can now be removed.

Change-Id: If47ef1958bf4de863995b9cfc042abf5bc849e24
Closes-Bug: 1297321
Merge "Add enable_security_group to BigSwitch and OneConvergence ini files"
Merge "ML2 Cisco Nexus MD: Remove workaround for bug 1276395"
Merge "Replace a usage of the deprecated root_helper option"