Session adapter doesn't update https connections cert data

Under a session, the first https request sets the HTTPSConnectionPool certs data.
If in a subsequent request, we change the certs data (eg: Set verify to True), the adaptor will update the ConnectionPool attributes, however each connection in the pool will still contain the old certs data, thus when requesting a connection from the pool, its info will differ from what we would expect.

Expected Result

The used connection should have updated certs data

Actual Result

The used connection have "old" certs data.

Reproduction Steps

These tests where performed against a server with a self-signed CA.

In [1]: from requests import Session

In [2]: url = "https://somepage"

In [3]: auth = ("admin", "admin123")

In [4]: s = Session()

In [5]: s.get(url, auth=auth, verify=False)

Out[5]: <Response [200]>

# This should fail, but doesnt
In [6]: s.get(url, auth=auth, verify=True)

Out[6]: <Response [200]>

# Create a new session
In [7]: Session().get(url, auth=auth, verify=True)
# Raises certificate verify failed

I'm aware ConnectionPool is in urllib realm, but since it's the adaptor who is updating the pool data, perhaps it should also handle this scenario?

System Information

{
"chardet": {
"version": "3.0.4"
},
"cryptography": {
"version": "1.7.2"
},
"idna": {
"version": "2.6"
},
"implementation": {
"name": "CPython",
"version": "2.7.12"
},
"platform": {
"release": "4.4.0-59-generic",
"system": "Linux"
},
"pyOpenSSL": {
"openssl_version": "1000207f",
"version": "16.0.0"
},
"requests": {
"version": "2.18.4"
},
"system_ssl": {
"version": "1000207f"
},
"urllib3": {
"version": "1.22"
},
"using_pyopenssl": true
}

Start by reproducing the two sequential HTTPS requests described in the issue, changing verify from False to True on the same Session. Trace the Session adapter's connection-pool updates and the pooled connections' certificate data; done means the reused connection reflects the updated certificate settings and the reported behavior is covered by a regression test.