Merge of CDM change:
https://widevine-internal-review.googlesource.com/#/c/10691/
This prevents the provisioning session from being created unless the
device needs provisioning. And then, after provisioning, it closes
the session it had previously opened.
b/15782159 CertificateProvisioning object keeps unused CryptoSession
Change-Id: Ic52ed864fa47c7ba50b7ca4d9fea1e74930228e9