When sending a build context to a remote server it may be (significantly) advantageous to compress the build context. This commit adds support for gz compression when constructing a build context using a command like "docker build --compress ." Signed-off-by: Paul Kehrer <paul.l.kehrer@gmail.com> Upstream-commit: 4825e58a96188e6a9c739c31966c8ac5a2bbd1d7 Component: engine