Reduce logging verbosity in NVIDIA Container Runtime

[elezar]

These changes reduce the verbosity of the logging of the NVIDIA Container Runtime -- especially for the case where no modifications are required.

See:

• https://github.com/containerd/containerd/issues/8972#issuecomment-2067595892
• https://github.com/NVIDIA/nvidia-container-toolkit/issues/511

Testing

1. Build the executable:

   make cmd-nvidia-container-runtime

2. Create a dummy config file:

   mkdir -p .config/nvidia-container-runtime
   cat <<EOF > .config/nvidia-container-runtime/config.toml 
   [nvidia-container-runtime]
   log-level = "info"
   runtimes = ["undefined", "missing", "runtime"]
   EOF

3. Create a dummy runtime:

   cat <<EOF > runtime
   #!/bin/bash
   echo "runtime args \$@"
   EOF
   chmod +x runtime

4. Run the NVIDIA runtime with the create command:

   PATH=$(pwd):${PATH} XDG_CONFIG_HOME=$(pwd)/.config \
   ./nvidia-container-runtime --log=$(pwd)/runtime.log create foo

5. Check the generated log:

   cat runtime.log

We can change the following:

• the log-level in the config file. Note that adding --debug flag to the command line (e.g. ./nvidia-container-runtime --debug) will configure debug logging.
• The runc command to check the behaviour for non-create commands.