Split fullstack test_securitygroup test case into small pieces

[Ihar Hrachyshka]

This is the description of the test case:

        """Tests if a security group rules are working, by confirming
        that 0. traffic is allowed when port security is disabled,
             1. connection from outside of allowed security group is blocked
             2. connection from allowed security group is permitted
             3. traffic not explicitly allowed (eg. ICMP) is blocked,
             4. a security group update takes effect,
             5. a remote security group member addition works, and
             6. an established connection stops by deleting a SG rule.
             7. multiple overlapping remote rules work,
             8. test other protocol functionality by using SCTP protocol
             9. test two vms with same mac on the same host in different
                networks

It shouldn't be like that. Each scenario should live in its own test case. Otherwise whenever something fails, it's hard to assess which step got us into broken state. The test case should be split into pieces.