build: Add a way for auto_build.py to print actions without executing

build: Add a way for auto_build.py to print actions without executing

[Mats Wichmann]

EXEC_MODE={one of: False, false, 0} python auto_build.py args
will print what the script would do without actually running the actions
Found it hard to keep track of all the different targets,
this is a quick way to report.

[Philippe Coval]

Port from master to 1.3-rel

Conflicts:
	auto_build.py

Change-Id: I6e03cc45ef4e51a5accde6f9866f7b62d3e002b7
Signed-off-by: Mats Wichmann <mats@linux.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/18635
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Dan Mihai <Daniel.Mihai@microsoft.com>
Bug: https://jira.iotivity.org/browse/IOT-1745
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/20789
Reviewed-by: George Nash <george.nash@intel.com>
Reviewed-by: Rick Bell <richard.s.bell@intel.com>