Add Temporary and DeleteTemporaryFiles to RuleBuilder

Temporary marks an output path as a temporary file that is not
necessary after the rule completes, removing it from the result of
Outputs.  DeleteTemporaryFiles adds a command to the command line
that deletes all files that have been marked with Temporary.

Test: rule_builder_test.go
Change-Id: Ie509ed800992962747fb287858e148e975eee54a