tests/run: Set a mode of 755 for the smoke binary
tests/run: Set a mode of 755 for the smoke binary

Avoiding:

  $ ./tests/run.sh
  ...
  cp: cannot create regular file ‘tectonic-dev/smoke’: Permission denied
  $ ls -l tectonic-dev/smoke
  -r-xr-xr-x. 1 trking trking 48972051 Sep 10 12:14 tectonic-dev/smoke

Ideally the Bazel output would have appropriate permissions by
default, but it currently provides no way to set write permission on
its output files [1].  With this commit, you can run run.sh multiple
times in succession without blowing away tectonic-dev between runs.

[1]: https://github.com/bazelbuild/bazel/issues/5588

derekhiggins/installer,derekhiggins/installer