Option for custom disk description implemented

[sri-srikanth]

Option to add a custom disk description implemented. Changes made in
ovirt_imageio/client/_ovirt.py's add_disk and
ovirt_imageio/client/upload.py's upload_disk to incorporate a
description variable, along with test/client_options_test.py to test
config and command line usage of the new custom description option.

Fixes #118
Signed-off-by: sri-srikanth srivatsansrikanth2018@gmail.com

[aesteve-rh]

Thanks for the contribution!

But you need to remove the unrelated commits (566a6de and 712d8a0), and squash the other two commits (05acb51 and 15e2bb2).

In the end, the PR should have a single commit with the correct implementation, including formatting and testing.

To do so, you can use interactive rebase (e.g. https://thoughtbot.com/blog/git-interactive-rebase-squash-amend-rewriting-history).
Something like this:

git rebase -i HEAD~4

Remove the lines of the unrelated commits and write s (for squash) in the last commit.
Save and close. That should do it. If something goes wrong with the rebase you can recover the status in the remote counterpart by doing:

git reset --hard origin/custom-disk-description

But if it did go well (as it should), you can just force push again:

git push -f

[sri-srikanth]

Removed unrelated commits, squashed relevant commits, and edited description :)

[aesteve-rh]

Updated the commit text to match the one in the PR.

I've resolved the comments. They were all addressed except for one minor comment for using a global variable. But at this point, it was not enough to make the PR go through another round after this much time.