Fix r_pkg_test
Fix r_pkg_test

We inadvertedly broke r_pkg_test which was now always passing because we
were supplying the wrong file path, and R exits with code 0 if it can
not find the file.

grailbio/rules_r,grailbio/rules_r,grailbio/rules_r,grailbio/rules_r,grailbio/rules_r