Fix invalidated PipelineCacheL2 pointer problem

Fix invalidated PipelineCacheL2 pointer problem

Let we keep std::list<PipelineCacheL2>::iterator instead of PipelineCacheL2*.

So, the pointer of pipeline what render-renderer has should be valid even
if cache container size changed.

And also, for safe issue, let we keep the pipeline container as std::list.

Change-Id: I5a0572f040ff3304876bdb2483af85ff26fbccbb
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>