upload.py: Fix immutable exception attribute.
upload.py: Fix immutable exception attribute.

BUG=chromium:356813
TEST=local
  - Actually failed login, watched error message get printed.

Review URL: https://codereview.chromium.org/1063143003

git-svn-id: fd409f4bdeea2bb50a5d34bb4d4bfc2046a5a3dd@294705 0039d316-1c4b-4281-b951-d872f2087c98

azureplus/chromium_depot_tools,liaorubei/depot_tools,npe9/depot_tools,azureplus/chromium_depot_tools,kaiix/depot_tools,hsharsha/depot_tools,ajohnson23/depot_tools,withtone/depot_tools,disigma/depot_tools,liaorubei/depot_tools,fracting/depot_tools,fracting/depot_tools,hsharsha/depot_tools,chinmaygarde/depot_tools,Midrya/chromium,hsharsha/depot_tools,aleonliao/depot_tools,primiano/depot_tools,disigma/depot_tools,CoherentLabs/depot_tools,mlufei/depot_tools,duanwujie/depot_tools,mlufei/depot_tools,azunite/chrome_build,SuYiling/chrome_depot_tools,disigma/depot_tools,aleonliao/depot_tools,kaiix/depot_tools,duongbaoduy/gtools,kaiix/depot_tools,npe9/depot_tools,duongbaoduy/gtools,cpanelli/-git-clone-https-chromium.googlesource.com-chromium-tools-depot_tools,SuYiling/chrome_depot_tools,primiano/depot_tools,duongbaoduy/gtools,cpanelli/-git-clone-https-chromium.googlesource.com-chromium-tools-depot_tools,chinmaygarde/depot_tools,gcodetogit/depot_tools,duanwujie/depot_tools,fracting/depot_tools,ajohnson23/depot_tools,SuYiling/chrome_depot_tools,azunite/chrome_build,npe9/depot_tools,Midrya/chromium,cpanelli/-git-clone-https-chromium.googlesource.com-chromium-tools-depot_tools,duanwujie/depot_tools,azureplus/chromium_depot_tools,mlufei/depot_tools,npe9/depot_tools,gcodetogit/depot_tools,liaorubei/depot_tools,gcodetogit/depot_tools,ajohnson23/depot_tools,aleonliao/depot_tools,azunite/chrome_build,chinmaygarde/depot_tools,CoherentLabs/depot_tools,withtone/depot_tools,liaorubei/depot_tools,Midrya/chromium,withtone/depot_tools,primiano/depot_tools