Add transcoder latency log for performance test

[lizhong1008]

add transcoder latency information to yami-utils

[xuguangxin]

Hi @lizhong1008
Could we keep this issue in libyami project? It helps us manage issues in one place and it's easy to track the issue in project page.

[lizhong1008]

@xuguangxin Daniel noticed this cases and I found there were some other issues created in yami-util so I moved it to here. Maybe we can discuss it with Daniel.

[xuguangxin]

Hi @lizhong1008
OK.

Hi @chivakker
Do you think it is ok to use one place to manager all features. It will help us tracking in project page https://github.com/01org/libyami/projects/2. It is one place for Lena to check all issues.