cubicweb #1330647 cubicweb-ctl : set stdout and stderr to be line buffered [validation pending]

As sysadmin, I wrap cubicweb-ctl commands in scripts which redirect stdout/stderr to files. I need such output to be flushed on a regular basis.

cubicweb-ctl needs to reopen the file descriptors (using os.fdopen) and force the buffering to "line buffered" (bufsize argument set to 0)

done in3.9.9
load left0.000
closed by<not specified>