@SdkTestInternalApi
    public static List<HttpClientConnectionManager> getRegisteredConnectionManagers() {
        return new ArrayList<HttpClientConnectionManager>(connectionManagers.keySet());
    }
Removes the given connection manager from this reaper,
and shutting down the reaper if there is zero connection manager left.

@return true if the connection manager has been successfully removed;
false otherwise.
aws-java-sdk-core/src/main/java/com/amazonaws/http/IdleConnectionReaper.java