Problem:
- sosreport currently creates a directory, put everything there THEN compress it
- This is CPU-intensive, involves an awful lot of unnecessary system calls, involves way more storage than necessary
- When a sosreport fails, users willing to provide files to their support team have to create the tarball themselves, when they know how to do that

Solution:
- Use Tarfile http://docs.python.org/library/tarfile.html
- Symlinks and commands outputs can be provided directly through TarFile.add() and TarInfo
- All signals need to be catched when possible, to make sure we have a consistent tarball

Positive effects:
- Less I/O, less operations
- A lot less disk space being used
- Virtually no temporary files

Negative effects:
- Back to gzip/bzip2 as TarFile does NOT expose the xz algorithm
-- or --
- Compression happens afterwards (partially defeats the purpose of this RFE)

Super-cool effect:
- (In the long term?) we can stop using /tmp and use the current directory.
- Users would have to be very explicitely notified about this change.

... Stuff I didn't think about yet, but please discuss in the comments.