etcd doesn't reload certs from disk when using ip address

[roboll]

When certificates change on disk, etcd should pick up new certificates on the next client/peer request. This does not always happen.

Based on the code here, if we set Certificates and clientHello.ServerName is empty (which is true when addressed via ip address), it will fall back to the first element of Certificates instead of calling GetCertificate.
https://github.com/golang/go/blob/master/src/crypto/tls/common.go#L716

According to this comment, the Certificates field needs to be set for integration tests to pass. I don't know why, but this is the cause of the issue. We should always be calling GetCertificates if certs should always be reloaded, never falling back to the certificate that was loaded at startup.
#7784 (comment)

[gyuho]

@roboll Good catch! I just confirmed that your fix #9542 resolves this issue:

CSR

...
  "CN": "s1",
  "hosts": [
    "127.0.0.1"
  ]
}

without localhost

fails but succeeds with that fix.

[gyuho]

We should be able to release the patch in 3.2 and 3.3 next week.