rpmbuild: replace "vmbuilder" base.
update vmbuilder.
rpmbuild: define "distro_dir" to use cached distro-tree.
rpmbuild: fix execscript path.
rpmbuild: set "rpm_dir" as environment variable.
rpmbuild: fix string check.
rpmbuild: set null hypervisor.
rpmbuild: fix arch type.
rpmbuild: remove unnecessary codes.
rpmbuild: remove unnecessary codes.
update code layout.
rpmbuild: remove unnecessary codes.
rpmbuild: merge rpmbuild.sh into spot-build.sh.
update code layout.
rpmbuild: remove unnecessary codes.
rpmbuild: use strict.
Revert "rpmbuild: use strict."

This reverts commit 37f1176bd9765551024fe5bba3de28d8131db725.
Revert "rpmbuild: remove unnecessary codes."

This reverts commit 8e5336b46975cc5ecd39804364708a6574c7b09b.
Revert "update code layout."

This reverts commit d01e8c284d83ec026889a6917229b865467aee5b.
Revert "rpmbuild: merge rpmbuild.sh into spot-build.sh."

This reverts commit e73c10c23704989cc33c3b080a1fa31e963a8c54.