log: Use sys._getframe() to avoid stat(2) calls

The Osmo MS driver is launching many many processes and I would
like to use the logging framework for the code as well.
Unfortunately the inspect/traceback code will use a linecache which
will execute stat(2) on one or more python files.

Related: OS#2927
Change-Id: I8f6bacadcf74d3aa25db1e1f41644f64aa19cf92
1 file changed