[sshfs] Multipass logs leaking filepaths from CI environments

In several compilation units, we are using the __FILE__ macro in logging messages. This is causing Multipass to leak file paths from our CI environment. i.e. [trace] [ssh process] /Users/cibot/actions-runner-2/_work/multipass-private/multipass-private/src/ssh/ssh_process.cpp:167 read_stream(type = 0, timeout = -1).

We should not be printing out the full path for the file. This part of the log message should either be removed or truncated to only include the top level src/ directory.