build: Reformat build_common SConscripts

build: Reformat build_common SConscripts

[Mats Wichmann]

build: Reformat all of the build_common SConscripts to be more Pythonic

There are not intended to be any functional changes.
The help variable definitions are split into multi-line,
in anticipation of later improving the descriptions and using
keyword-argument style to make the purpose of other args more clear.

Also included two files at the top level in this set,
as they seem to have the same intent as build_common.

In build_common/android/SConscript, an identical 4-line stanza, beginning:
  elif cmp(flags[0:9], 'PLATFORM=') == 0:  # get target platform: android-x
appears three times, the second and third were dropped in this change.

[Philippe Coval]

Port from master to 1.3-rel to help mergeback

Conflicts:
	build_common/SConscript
	build_common/android/SConscript
	build_common/external_builders.scons
	build_common/linux/SConscript

Change-Id: I0077e7350754fef25e75621fdb4a41cfcf28ef2a
Signed-off-by: Mats Wichmann <mats@linux.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/20545
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: George Nash <george.nash@intel.com>
Reviewed-by: Phil Coval <philippe.coval@osg.samsung.com>
Origin: master
Bug: https://jira.iotivity.org/browse/IOT-1745
Signed-off-by: Phil Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/20923
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>