Add scope name  to console while printing goal help

Right now,
./pants goal compile --help shows

compile: Scala source code style check.

-h, --help   show this help message and exit
--[no-]skip  Skip scalastyle. (default: None)

-h, --help              show this help message and exit
--partition-size-hint <# source files>
                        Roughly how many source files to attempt to compile
                        together. Set to a large number to compile all sources
                        together. Set to 0 to compile target-by-target.
                        (default: 9223372036854775807)
--[no-]warnings         Compile with all configured warnings enabled.
                        (default: True)
--missing-deps {off,warn,fatal}
.
.
--plugins _COMPILE.SCALA_PLUGINS__
                        Use these scalac plugins. (default: [])

-h, --help              show this help message and exit
--partition-size-hint <# source files>
                        Roughly how many source files to attempt to compile
                        together. Set to a large number to compile all sources
                        together. Set to 0 to compile target-by-target.
                        (default: 9223372036854775807)
--[no-]warnings         Compile with all configured warnings enabled.
                        (default: True)
--missing-deps {off,warn,fatal}
                        Check for missing dependencies in java code. Reports
                        actual dependencies A -> B where there is no

.
.
--[no-]delete-scratch   Leave intermediate scratch files around, for debugging
                        build problems. (default: True)
--args _COMPILE.APT_ARGS__
                        Pass these extra args to javac. (default: [])
.
.
-h, --help              show this help message and exit
--partition-size-hint <# source files>
                        Roughly how many source files to attempt to compile
                        together. Set to a large number to compile all sources
                        together. Set to 0 to compile target-by-target.
                        (default: 9223372036854775807)
--[no-]warnings         Compile with all configured warnings enabled.
                        (default: True)

This is very confusing,
Plus does not show the sub tasks in this goals and hence anyone wanting to use task specific option has no idea how to.

@Benjy let me know if this was intentional.

Testing Done:
yes.
You can see the tasks in the compile goal.

./pants goal compile --help

/Users/tdesai/projects/pants/dist/pants_local_binary.pex -> /Users/tdesai/projects/pants/pants.pex

compile: Scala source code style check.

compile.scalastyle
  -h, --help   show this help message and exit
  --[no-]skip  Skip scalastyle. (default: None)
compile.scala
  -h, --help              show this help message and exit
  --partition-size-hint <# source files>
                          Roughly how many source files to attempt to compile
                          together. Set to a large number to compile all sources
                          together. Set to 0 to compile target-by-target.
                          (default: 9223372036854775807)
  --[no-]warnings         Compile with all configured warnings enabled.
                          (default: True)

..
compile.apt
  -h, --help              show this help message and exit

..
  --args _COMPILE.APT_ARGS__
                          Pass these extra args to javac. (default: [])
compile.java
  -h, --help              show this help message and exit
  --partition-size-hint <# source files>

Reviewed at https://rbcommons.com/s/twitter/r/1375/
Sync of https://github.com/pantsbuild/pants/commit/3a9553f71b5747a645ecfd57c7a1a5b74df121e5