Report out-of-space, not patch-invalid

(Small fix on top of Mike's pull-reqest #1598 as described below. This pull-req supersedes that one.)

If there isn't enough space on the filesystem to upload a patch (which can take
2-3 times the size of the patch, because of multiple copies and gpg signature
checking), we should fail with an Out_of_space exception. Before, if the gpg
check failed because there wasn't enough space to write the unsigned cleartext,
we would erroneously report patch_invalid. Now we check that there is enough
free space to signature check the patch (we make a guess of 2 * size of the
patch), and catch Unix.ENOSPC exceptions and handle them accordingly.

CA-124008

Signed-off-by: Mike McClurg mike.mcclurg@citrix.com