Sandbox genrule tools

Copy tools used by genrules into the sandbox directory.  This
ensures correct dependencies on all files used by tools, and
is one step closer to enabling genrules inside unselected
namespaces.

Bug: 124313442
Test: genrule_test.go
Test: rule_builder_test.go
Test: m checkbuild
Change-Id: I38393900677c5dbe8e72fe06a7dd7d71f3c09f82