libprocessgroup: Make a log message more detailed

For log messages like the following it is not possible to derive why
this message has been logged:

E libprocessgroup: AddTidToCgroup failed to write '3949'; fd=55: Operation not supported on transport endpoint

Hence include the cgroup path and the tid type in the log message.

Change-Id: I057711fe576b82f6454456b7284186ddeece33c3
Signed-off-by: Bart Van Assche <bvanassche@google.com>