common: Enable log system

Use export LIBYAMI_LOG_LEVEL=log_level to set the control flag, export LIBYAMI_TRACE=log_file to set the file location

Signed-off-by: Tang Xin <xin.t.tang@intel.com>
I think log with user specified name is better.
for example, i want to compare the log from 2 yami clients. one is from omx, another is unit test.