REGTESTS: checks: Fix tls_health_checks when IPv6 addresses are used

REGTESTS: checks: Fix tls_health_checks when IPv6 addresses are used

In tls_health_checks.vtc, when IPv6 addresses are used, A config error is
reported because of the "addr" server parameter. Because there is no specified
port, the IPv6 address must be enclosed into brackets to be properly parsed. It
also works with IPv4 addresses. But instead, a dummy port is added to the addr
parameter. This way, we also check the port parameter, when specified, is used
in priority over the port found in the addr parameter.

This patch should fix the issue #646.