Currently we are doing fmt.sprintf on hostname and port which will not properly handle ipv6 addresses, instead of changing pangolin to send bracketed address a simply net.join can do this for us since we dont need to parse a formatted string
Add the Server Name Indication (SNI) field to healthcheck requests, if
present in the target config.
SNI handling is already present for proxying resources, but this has
not been implemented for healthcheck requests yet until this commit.
In order to facilitate this, this commit moves the client instantiation
to when the healthcheck is performed, rather than as a part of the
monitor init.
