[SPARK-1275] Made dev/run-tests executable.

This was causing Jenkins tests to fail for PRs against branch 0.9.

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #178 from tdas/branch-0.9-fix and squashes the following commits:

a633bce [Tathagata Das] Merge remote-tracking branch 'apache-github/branch-0.9' into branch-0.9-fix
9b043cc [Tathagata Das] Made dev/run-tests executable.