HTTPS connection fails with SSL ERROR: BAD_ECC_CERT

There is apparently a bug with the **openssl** library or configuration here in this python module, such that connections with HTTPS to **etcd v3 server** fail with an error like this.

`E0607 12:43:00.193069658 11623 ssl_transport_security.cc:1238] Handshake failed with fatal error SSL_ERROR_SSL: error:1000006b:SSL routines:OPENSSL_internal:BAD_ECC_CERT.`

This is reported as [GRPC Issue 6722](https://github.com/grpc/grpc/issues/6722). The workaround is to generate different x509 certs with the downgraded "P-Curve" algorithm of P-256 instead of P-384. Instead, it would be awesome to get this bug fixed here so the workaround is not required.

P.S. My local openssl installation appears current. If that has anything to do with this, I'm all ears.

Start by reproducing an HTTPS connection from this Python module to an etcd v3 server using the reported P-384 certificate and compare it with the P-256 workaround. Read the linked gRPC issue and inspect the module's OpenSSL or connection configuration. Done means the P-384 certificate connects successfully without requiring downgraded certificates.

Written by the indexing model from the issue text.