test: check ipv6 support before testing it

fix #7983
fix #8049

Conflicts:
	test/common.js
tests: don't assume IPv4 only in remote addr tests

Tests in test-net-remote-address-port.js assume that client and server
sockets always use IPv4. However, depending on the OS and the network
interfaces setup, this is not true. This change makes the test consider
that both IPv4 or IPv6 sockets are valid

Fixes #8096.