Only push coverage from one case in the test matrix.

Echo the command.
Install all possible dependencies with conda.
Use MPICH2 for testing on Travis.
Test for MPICH2.
Merge pull request #517 from enthought/bugfix/coverage-reporting

Only push coverage from one case in the test matrix.
Merge pull request #519 from enthought/feature/use-mpich2

Allow testing with MPICH2
Merge branch 'master' into refactor/small-cleanup