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>

contrib/completion/bash/docker

@@ -758,6 +758,7 @@ _docker_build() {
 	"
 
 	local boolean_options="
+		--compress
 		--disable-content-trust=false
 		--force-rm
 		--help

contrib/completion/zsh/_docker

@@ -1509,6 +1509,7 @@ __docker_subcommand() {
                 $opts_build_create_run \
                 $opts_build_create_run_update \
                 "($help)*--build-arg[Build-time variables]:<varname>=<value>: " \
+                "($help)--compress[Compress the build context using gzip]" \
                 "($help -f --file)"{-f=,--file=}"[Name of the Dockerfile]:Dockerfile:_files" \
                 "($help)--force-rm[Always remove intermediate containers]" \
                 "($help)*--label=[Set metadata for an image]:label=value: " \

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)

man/docker-build.1.md

@@ -16,6 +16,7 @@ docker-build - Build a new image from the source code at PATH
 [**--label**[=*[]*]]
 [**--no-cache**]
 [**--pull**]
+[**--compress**]
 [**-q**|**--quiet**]
 [**--rm**[=*true*]]
 [**-t**|**--tag**[=*[]*]]
@@ -84,6 +85,9 @@ set as the **URL**, the repository is cloned locally and then sent as the contex
 **--pull**=*true*|*false*
    Always attempt to pull a newer version of the image. The default is *false*.
 
+**--compress**=*true*|*false*
+    Compress the build context using gzip. The default is *false*.
+
 **-q**, **--quiet**=*true*|*false*
    Suppress the build output and print image ID on success. The default is *false*.