Fix cover file saving with /tmp on different FS

[kevinoid]

If the directory used by tempfile.NamedTemporaryFile is on a different filesystem (e.g. /tmp on tmpfs), whipper cd rip --cover-art will fail with an error such as:

Traceback (most recent call last):
  File "/usr/bin/whipper", line 11, in <module>
    load_entry_point('whipper==0.9.0', 'console_scripts', 'whipper')()
  File "/home/kevin/tmp/whipper/whipper/command/main.py", line 43, in main
    ret = cmd.do()
  File "/home/kevin/tmp/whipper/whipper/command/basecommand.py", line 139, in do
    return self.cmd.do()
  File "/home/kevin/tmp/whipper/whipper/command/basecommand.py", line 139, in do
    return self.cmd.do()
  File "/home/kevin/tmp/whipper/whipper/command/cd.py", line 191, in do
    self.doCommand()
  File "/home/kevin/tmp/whipper/whipper/command/cd.py", line 363, in doCommand
    self.program.metadata.mbid)
  File "/home/kevin/tmp/whipper/whipper/common/program.py", line 498, in getCoverArt
    os.replace(f.name, cover_art_path)
OSError: [Errno 18] Invalid cross-device link: '/tmp/tmprmx4d9c9.cover.jpg' -> './Boston/Greatest Hits/cover.jpg'

due to calling os.replace with paths on different filesystems.

Instead of os.replace, this PR uses shutil.move, which falls back to shutil.copy2 if os.replace doesn't work.

Thanks for considering,
Kevin

[JoeLametta]

Merged, thanks!
I need to check whether os.replace / os.rename has been used in other places in a similar (wrong) way.

[kevinoid]

Thanks for reviewing and merging!

Good thought looking for similar issues. Mounting a separate tmpfs on $HOME/.config/whipper, $TEMP, working_directory, and output_directory might be a reasonable smoke test. Not sure if you want to bother supporting more pathological cases (e.g. album directory mounted on different FS).

[JoeLametta]

Hi, I've just replaced all occurrences I've found in whipper of os.replace and os.rename with shutil.move (in commit b39345e).

[kevinoid]

Great, thanks @JoeLametta!