Create general certificate provisioning tests

Creates parameterized certificate provisioning tests to prepare for DRM
reprovisioning implementation.
- Create parameterized certificate provisioning test suite.
- Change RETURN_IF_NOT_OPEN macro to call IsOpen instead of checking
  the |open_| variable to make mocking of CryptoSession methods easier.

Bug: b/305093063
Merged from https://widevine-internal-review.googlesource.com/188051

Change-Id: Ic1c344af64073a8ff5626530a0864bfeea90fc6e

libwvdrmengine/cdm/core/include/certificate_provisioning.h

@@ -73,6 +73,9 @@ class CertificateProvisioning {
   static void GetProvisioningServerUrl(std::string* default_url);
 
  private:
+#if defined(UNIT_TEST)
+  friend class CertificateProvisioningTest;
+#endif
   CdmResponseType GetProvisioningRequestInternal(
       wvutil::FileSystem* file_system,
       RequestedSecurityLevel requested_security_level,