coverity: report errors when uploading tarball
coverity: report errors when uploading tarball

Curl by default does not report errors by setting the error code.
As the upload can fail through several conditions (e.g. the rate
limit, leading to unauthorized access) we should indicate this
information in Travis CI.

To improve upon the behavior, use `--write-out=%{http_code}` to
write out the HTTP code in addition to the received body and
return an error if the code does not equal 201.

saurabhsuniljain/libgit2,jeffhostetler/public_libgit2,jeffhostetler/public_libgit2,jeffhostetler/public_libgit2,leoyanggit/libgit2,joshtriplett/libgit2,Corillian/libgit2,stewid/libgit2,stewid/libgit2,jeffhostetler/public_libgit2,leoyanggit/libgit2,Corillian/libgit2,joshtriplett/libgit2,leoyanggit/libgit2,joshtriplett/libgit2,leoyanggit/libgit2,joshtriplett/libgit2,saurabhsuniljain/libgit2,jeffhostetler/public_libgit2,stewid/libgit2,leoyanggit/libgit2,stewid/libgit2,saurabhsuniljain/libgit2,leoyanggit/libgit2,saurabhsuniljain/libgit2,Corillian/libgit2,stewid/libgit2,Corillian/libgit2,jeffhostetler/public_libgit2,Corillian/libgit2,joshtriplett/libgit2,joshtriplett/libgit2,Corillian/libgit2,saurabhsuniljain/libgit2,stewid/libgit2,saurabhsuniljain/libgit2