Fix set command line options for ANDROID_XXX into scons environment.

Fix set command line options for ANDROID_XXX into scons environment.

Due to this the android SDK, NDK and Gradle were downloaded even if
the options are specified on commandline.

Change-Id: I00564d62c8374b73f3b4b75b7d75735d0a49f16f
Signed-off-by: Ashwini Kumar <k.ashwini@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1513
Reviewed-by: Joseph Morrow <joseph.l.morrow@intel.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Erich Keane <erich.keane@intel.com>