Error out if trace already exists unless 'append' option is used

[christophebedard]

Closes #12

This makes the ros2 trace command and the Trace launch action fail if the trace already exists, unless the --append-trace or append_trace/append-trace option is used, respectively. Example:

$ ros2 trace -s 'my-trace'  # Generate trace
UST tracing enabled (28 events)
kernel tracing disabled
context (3 fields)
writing tracing session to: /home/chris/.ros/tracing/my-trace
press enter to start...
press enter to stop...
stopping & destroying tracing session
$ ros2 trace -s 'my-trace'  # Mistakenly append to existing trace, error out
UST tracing enabled (28 events)
kernel tracing disabled
context (3 fields)
writing tracing session to: /home/chris/.ros/tracing/my-trace
press enter to start...
error: trace directory already exists, use the append option to append to it: /home/chris/.ros/tracing/my-trace
$ ros2 trace -s 'my-trace' --append-trace   # Use '--append-trace' option, all good
UST tracing enabled (28 events)
kernel tracing disabled
context (3 fields)
writing tracing session to: /home/chris/.ros/tracing/my-trace
press enter to start...
press enter to stop...
stopping & destroying tracing session

I've also added tests to cover it in both ros2trace and test_tracetools_launch. I added a simple test for the existing append_timestamp Trace launch action option to test_tracetools_launch as well.

Signed-off-by: Christophe Bedard christophe.bedard@apex.ai

[christophebedard]

Testing --packages-above ros2trace tracetools_launch tracetools_trace:

• Linux
• Linux-aarch64
• Windows

[mjcarroll]

LGTM with green CI!