LBaaS UT: use constants vs magic numbers for http error codes

Closes-Bug: #1245388
Change-Id: I4192b577182891f6d777a5a5eac237c9961e41bb
Adds delete of a extra_dhcp_opt on a port

Add support for delete of extra_dhcp_opt(s) on a port. Where
[{'opt_name': 'opt_to_delete', 'opt_value': None}].

Closes-Bug: #1228008

Change-Id: I75baeff91575cac6546fe2cc6fcf7a0d8e92853f
Merge "LBaaS UT: use constants vs magic numbers for http error codes"
Merge "Adds delete of a extra_dhcp_opt on a port"