Properly close plugins on SIGTERM and exit

test: adb reboot while playing netflix and check logcat
  to make sure session are closed.

[ Merge of http://go/wvgerrit/133063 ]

bug: 193099676
Change-Id: I375695673b0c366e09fb857f5ae7a9cb6b946779

libwvdrmengine/mediadrm/src_hidl/WVDrmPlugin.cpp

@@ -196,10 +196,17 @@ WVDrmPlugin::WVDrmPlugin(const sp<WvContentDecryptionModule>& cdm,
     mCDM(cdm),
     mCrypto(crypto),
     mCryptoSessions(),
-    mAppPackageName(appPackageName) {}
+    mAppPackageName(appPackageName) {
+  Terminator::Register(this);
+}
 
 WVDrmPlugin::~WVDrmPlugin() {
   wvcdm::SetLoggingUid(mCdmIdentifierBuilder.user_id());
+  Terminator::Forget(this);
+  Close();
+}
+
+void WVDrmPlugin::Close() {
   typedef map<CdmSessionId, CryptoSession>::iterator mapIterator;
   for (mapIterator iter = mCryptoSessions.begin();
        iter != mCryptoSessions.end();