Added log_path variable in containers/common, User sets default log path in containers.conf under the `[containers]` section.
The directory has to exist beforehand. Container logs go under this directory, sub-directories named with the container id
and inside the sub-directory a ctr.log file will be created where the container logs for the corresponding container will go.
This path can be overridden by using the `--log-opt` flag.
Signed-off-by: Joshua Arrevillaga <2004jarrevillaga@gmail.com>