android: fix location of sdk

android: fix location of sdk

The file android-sdk_r24.2-linux.tgz contains a directory named android-
sdk-linux and the macos and windows version use similar directory names.

This fixes the following error message:
/iotivity/extlibs/android/gradle/gradle-2.2.1/bin/gradle build -b/iotivity/android/android_api/build.gradle -PTARGET_ARCH=armeabi -PRELEASE=release

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring project ':base'.
> The SDK directory '/iotivity/extlibs/android/sdk/android-sdk_r24.2' does not exist.

This was only tested under Linux and not tested under windows or macos.

Change-Id: Ia316ed65dc22f653a297b6423d4e1b47a24c8dbe
Signed-off-by: Hauke Mehrtens <hauke.mehrtens@lantiq.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1222
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>