Moved build-check and build-clean scripts to buildtools dir so

that they can be used for normal builds too (not just release
builds).

diff --git a/releasetools/build-check b/buildtools/build-check
similarity index 100%
rename from releasetools/build-check
rename to buildtools/build-check

diff --git a/releasetools/build-clean b/buildtools/build-clean
similarity index 100%
rename from releasetools/build-clean
rename to buildtools/build-clean