Put log file in 'release' output always.

Put log file in 'release' output always.

When image creation failed, log created by '--release' will be
located under 'outdir' instead of 'release_dir'. Also put the
log file under 'release_dir' when image creation failed.

mic-appliance create images through executing '/etc/init.d/mic'
script in the appliance. 'time mic cr auto $extra /media/out/$ks'
is called, and '--release' option is used when creating images.

In the past, 3 points about the logfile created by '--release':
1. Create logfile in default 'out_dir' which is specified in
'/etc/mic/mic.conf'. 2. Before creating images, check whether the
'release_dir' exists, if it exists, remove the whole directory. 3.
After the image creation finished, copy the logfile to the final
'release_dir' where the images located. So when the image creation
failed, no logfile found in 'release_dir', the logfile is under default
'out_dir'.

If directly change the 'out_dir' to 'dest_dir' in conf.py, the image
creation will fail if there already exist a same 'release_dir', because
this existed 'release_dir' will be removed when creating images, but the
logfile use this dir at the time, so it cannot be removed, then mic will
fail and exit. So right now, if 'release_dir' already existed, just remove
the files under it except the newly created logfile, and remain the dir.

Fixes: #2212

Change-Id: Ibdc9af3d0e03ca966517d05b1e519d4d9fb3ad43