Use string, not repr, for log reporting PosixPath
Fix for #40002 (closed) introduced a small formatting issue in Chutney's log output, e.g.:
NOTE: creating PosixPath('/home/c/git/tor/../chutney/net/nodes.1596403717'), linking to PosixPath('/home/c/git/tor/../chutney/net/nodes')
Easy enough fix, I just need to make log output refer to the string expression of PosixPath
s rather than the representation.