Make 'docker build' send non-err output to stdout

Right now 'docker build' will send:
   Sending build context to Docker daemon
to stderr, instead of stdout.  This PR fixes that.

I looked in the rest of api/client/commands.go for other cases
that might do this and only one jumped out at me:
  https://github.com/docker/docker/blob/master/api/client/commands.go#L2202
but I think if I changed that to go to stdout then it'll mess people up
who are expecting just the container ID to be printed to the screen and
there is no --quiet type of flag we can check.

Closes #9404

Signed-off-by: Doug Davis <dug@us.ibm.com>
Merge pull request #9512 from duglin/Issue9404

Make 'docker build' send non-err output to stdout
Merge remote-tracking branch 'origin/master' into bump_v1.4.0

* origin/master: (530 commits)
  Removed race condition If two interrupts were fired really quickly interruptCount could have been incremented twice before the LoadUint32 making cleanup not being called at all.
  Return docker's root dir in docker -D info
  I was talking to someone whom i listen to, and she noted that our docs don't mention the license
  Show image of the Build trigger screen, and add a little search engine fodder for it.
  Add some extra details to webhook docs
  this v spacing irritated me while i was reading
  Auto-update documentation from the output of the cli.
  Make 'docker build' send non-err output to stdout
  Use consistent ApplyLayer in overlayfs
  Update Amazon EC2 Docker installation instructions
  Fixing docs formatting for the forcerm flag on docker build
  Fix interactive exec over TLS
  Correctly close generated benchmark archives
  Something changed, broke the docs release script, and it seems that --exclude still doesn't work, so I'm removing it
  Fix output format where no variable specified in mount pkg
  Run 'go vet' on integration-cli.
  Remove unnessary abstraction deepEqual
  Note that using -lxc-conf to change things Docker manages has pitfalls
  Remove unnecessary abstraction nLines
  cleanup: remove startCommand function, only used once, and unecessary abstraction.
  ...

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
Bump version to v1.4.0

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)