Add support for compressing build context during image build

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

components/engine/docs/reference/commandline/build.md

@@ -19,6 +19,7 @@ Options:
       --build-arg value         Set build-time variables (default [])
       --cache-from value        Images to consider as cache sources (default [])
       --cgroup-parent string    Optional parent cgroup for the container
+      --compress                Compress the build context using gzip
       --cpu-period int          Limit the CPU CFS (Completely Fair Scheduler) period
       --cpu-quota int           Limit the CPU CFS (Completely Fair Scheduler) quota
   -c, --cpu-shares int          CPU shares (relative weight)