tools: only create log file when requested

tools: only create log file when requested

We used to initialize a log unconditionally before. This has led to scenarios
where users where left with container directories and an empty log file even
though they didn't request a log be created at all.
Switch all tools to only create a log file when the user explicitly requests
this.

Closes #1779.
Closes #2032.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>