build: Clean build folders when using scons -c

build: Clean build folders when using scons -c

Since Android and Java code is built using gradle
the build output is not properly tracked by scons.
Scons' Clean method is used to add the build
output to the clean build.

This commit is limited to the `build` folders
generated when building TARGET_OS=android or
BUILD_JAVA=1.

Change-Id: I69965272e377494bd99731fbacb2cc6e06ff7815
Signed-off-by: George Nash <george.nash@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/16977
Tested-by: jenkins-iotivity <jenkins@iotivity.org>
Reviewed-by: Larry Sachs <larry.j.sachs@intel.com>
Reviewed-by: Rick Bell <richard.s.bell@intel.com>