MediaExtractor: Add more skip conditions for the second-pass extractors

If the stream's container is opaque (DRM) or a known skip condition
(cached-source MPEG4), don't push it through the deep scanner

Change-Id: Ia9d60180b5d177714d206fc7dc94da93b37a048e
Merge pull request #7 from CyanogenMod/cm-11.0

MediaExtractor: Add more skip conditions for the second-pass extractors