According to help `swift upload -h` you can add a customized request header 'Content-Type'.
But actually it is ignored (cleared and default is used) if subcommand is upload.
Subcommand post works as expected in help.
Bug fix: Use 'Content-Type' from the customized request headers also if
uploading.
Change-Id: If0d1354b6214b909527341078fe1769aa6587457