Fix SSL tests due to verifier behavior changes in OpenSSL 1.1.1i

Summary:
Some tests were relying on internal OpenSSL behavior that changed in OpenSSL
1.1.1i.

OpenSSL commit [2e06150e](https://github.com/openssl/openssl/commit/2e06150e3928daa06d5ff70c32bffad8088ebe58)
causes additional `handshakeVer` callback invocations. If an UNABLE_TO_VERIFY_LEAF_SIGNATURE handshakeVer
callback overrides the result to *true*, OpenSSL will now continue to perform certificate
verifications **as if the overriden cert was the properly found root**. This means:

* It is subject to certificate expiration checks, and,
* A final `handshakeVer` callback is invoked with `preverifyOk=1` when it passes the expiration checks.

Several of our tests that relied on `handshakeVer` only being called *once* broke. Since the tests
are testing a different, higher level aspect of verification (i.e. it is not actually trying to
test how many times `handshakeVer` is being called), I've relaxed some of the expectations to allow
for multiple invocations.

CertificateVerifier semantics were also affected. Because there is a final
successful `handshakeVer` callback that is issued, it is not just sufficient
to check for depth and preverifyOk before invoking the CertificateVerifier.

Reviewed By: pixelb

Differential Revision: D25775429

fbshipit-source-id: 98d35249a623307fb1de366c498b1dbae4fabf82

folly/io/async/test/AsyncSSLSocketTest.h

@@ -1260,6 +1260,7 @@ class SSLHandshakeBase : public AsyncSSLSocket::HandshakeCB,
   bool handshakeVerify_;
   bool handshakeSuccess_;
   bool handshakeError_;
+  int handshakeVerifyInvocations_{};
   std::chrono::nanoseconds handshakeTime;
 
  protected:
@@ -1272,9 +1273,12 @@ class SSLHandshakeBase : public AsyncSSLSocket::HandshakeCB,
       AsyncSSLSocket* /* sock */,
       bool preverifyOk,
       X509_STORE_CTX* /* ctx */) noexcept override {
-    handshakeVerify_ = true;
+    auto invocation = handshakeVerifyInvocations_++;
 
-    EXPECT_EQ(preverifyResult_, preverifyOk);
+    if (invocation == 0) {
+      handshakeVerify_ = true;
+      EXPECT_EQ(preverifyResult_, preverifyOk);
+    }
     return verifyResult_;
   }