allow insecureSkipTlsVerify with certificates

[iFission]

use case:
skip hostname verification

code allows for both insecureSkipTlsVerify and certs:

kafka_exporter/kafka_exporter.go

Line 215 in 2e60c05

InsecureSkipVerify: opts.tlsInsecureSkipTLSVerify,

		config.Net.TLS.Config = &tls.Config{
			ServerName:         opts.tlsServerName,
			InsecureSkipVerify: opts.tlsInsecureSkipTLSVerify,
		}