aws: s3hlssink: Fix deadlock on EOS and usage with hlssink3

• aws/s3hlssink: Use factory name when checking name of child element
  Commit ad3f1cf5 fixed the name of hlssink child element to be the same for hlssink2 and hlssink3. However, we rely on element name to return boolean in case of hlssink3 or None in case of hlssink2 as the return value of the delete-fragment closure.

  Fix this by using the factory name instead of the element name.

• aws/s3hlssink: Fix deadlock on EOS
  In state change to NULL, we take state lock and call stop. When stop is called, we will try to upload queued segments in S3 request thread. That tries to take the state lock again and deadlocks.

CC: @arun