droptailer client cannot send data

[majst01]

Dec 03 20:27:09 shoot--pcfgbt--gerrit-firewall-1afab ip[106868]: 2020/12/03 20:27:09 unable to send dropentry:rpc error: code = Unavailable desc = connection error: desc = "transport: authentication handshake failed: x509: certificate relies on legacy Common Name field, use SANs or temporarily enable Common Name matching with GODEBUG=x509ignoreCN=0"
Dec 03 20:27:12 shoot--pcfgbt--gerrit-firewall-1afab ip[106868]: 2020/12/03 20:27:12 unable to send dropentry:rpc error: code = Unavailable desc = connection error: desc = "transport: authentication handshake failed: x509: certificate relies on legacy Common Name field, use SANs or temporarily enable Common Name matching with GODEBUG=x509ignoreCN=0"

Seems to be related to go 1.15
jaegertracing/jaeger#2435, this points to the real solution:
golang/go#39568 (comment)

adding:

Environment=GODEBUG=x509ignoreCN=0

to droptailer.service immediatly makes the connection work again

I think we must change the way the certs are create in https://github.com/metal-stack/gardener-extension-provider-metal

@mwindower we must fix this with the next fw image version.

[majst01]

According to golang/go#39568 (comment)

We must add DNSNames here:
https://github.com/metal-stack/gardener-extension-provider-metal/blob/master/pkg/controller/controlplane/valuesprovider.go#L666