Remove python25 workaround from glance_http

Since we don't support python25 removing to reduce what to cover in the
unittests.
Also fix a problem with a possible NoneType in the right side of the comparison
cause an exception. Now the default value for content-type header is an empty
string.

Change-Id: I3df5ac75455e62689f08c336fc89a0437dae6945
Check attributes of create/delete sec groups rule

This patch adds the JSON schema for Nova V2 create/delete security
groups rule APIs response and validate the response with added
JSON schema to block the backward incompatibility change in the future.

The response body of v2 create security groups rule API is the below:

{
    "security_group_rule": {
        "from_port": 80,
        "to_port": 80,
        "group": {},
        "ip_protocol": "TCP",
        "parent_group_id": 5,
        "id": 1,
        "ip_range":{
            "cidr": "10.10.10.0/24"
        }
    }
}

Partially implements blueprint nova-api-attribute-test

Change-Id: I8e85b3da74a2a5d4b16c3e33429c0b4d0da0c1c9
Merge "Check attributes of create/delete sec groups rule"
Merge "Remove python25 workaround from glance_http"