test: add/delete SG members

[jerome-jutteau]

Initial setup:

• Machine A security group: SG1
• Machine B security group: SG2
• SG1 members: A's IP
• SG2 members: B's IP
• SG1 rule: Allow all members of SG1 to access UDP port 8000
• SG2 rule: Allow all members of SG2 to access UDP port 9000

Tests that:

• machine A can't speak with B on UDP port 9000.
• machine B can't speak with A on UDP port 8000.

Change setup:

• SG1: members: add B's IP
• SG2: members: add A's IP

Test that:

• machine A can speak with B on UDP port 9000.
• machine B can speak with A on UDP port 8000.

Change setup:

• SG1: members: remove B's IP
• SG2: members: remove A's IP

Test that:

• machine A can't speak with B on UDP port 9000.
• machine B can't speak with A on UDP port 8000.