Steps to reproduce the issue

1. Add openmpi as an external package
2. Run spack test openmpi
3. Test fails because examples directory isn't found in installation prefix

Error Message

Command exited with status 2:
    '/usr/bin/make' 'all'
make: *** No rule to make target `all'.  Stop.

Recommended Solution

We should skip tests for external packages that require additional files.

Information on your system

• Spack: 0.14.1-6842-6f534ac
• Python: 3.6.8
• Platform: linux-centos7-haswell
• Concretizer: original

packages:
  openmpi:
    buildable: false
    externals:
    - spec: [email protected]%[email protected]
      modules:
      - gnu/openmpi-3.1.6-gnu-9.3.0

Additional information

• I have run spack debug report and reported the version of Spack/Python/Platform
• I have searched the issues of this repo and believe this is not a duplicate
• I have run the failing commands in debug mode and reported the output