Run tests after creating a tarball

This avoids problems where we forgot to update MANIFEST.in or
setup.py when adding new files.

(cherry picked from commit e47c84278ec8b279bd699b46d5fdf051efc258c2)

Change-Id: I41220a0a385226262481c99a44ae8b0cd15e34fb
Merge "Run tests after creating a tarball" into 1.7