Revert "add eventlet to test requirement"

This reverts commit e93a3f2d99133422e51fbd531dd58052e8e261a3.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Support bind IPv6 addresses in StreamServer

Use a very loose condition to determine if the address is an IPv6
address or not.

Signed-off-by: Can Zhang <can@canx.me>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>