[cli] Lift artificial limitation on --build-arg
[cli] Lift artificial limitation on --build-arg

Currently, `docker-compose --build-arg` requires that a service be
specified as part of the command-line invocation. So,

  $ docker-compose build --build-arg nocache=`git rev-parse @` foom

works. However, when using out-of-band scripts to automate the build
process of several Docker containers (in a CI system, for instance), it
becomes difficult to specify exactly which service requires the
build-arg. Docker has supported Dockerfiles that ignore build-args for a
long time, so there is no problem is specifying spurious build-args to
builds that don't consume it.

The limitation on `docker-compose build` today is artificial, and there
are no other commands that require specifying a service. Allow
`--build-arg` to also match all services so this is possible:

  $ docker-compose build --build-arg nocache=`git rev-parse @`

Please refer to #3790 for discussion on the original feature.

Signed-off-by: Ramkumar Ramachandra <5c355d1d38066ed0c5de420d67c1b5ed0687c4bd@gmail.com>

thaJeztah/compose,vdemeester/compose,dnephin/compose,funkyfuture/docker-compose,vdemeester/compose,shin-/compose,thaJeztah/compose,dnephin/compose,shin-/compose,funkyfuture/docker-compose