stack haddock ignores the dependencies of test suites and executables

### General summary/comments (optional)

`stack haddock` generates the documentation for the dependencies of the library component, but not of the executable or test components.
### Steps to reproduce
1. Create a cabal package where some packages are required by the executable or test but not the library
2. Run `stack haddock`
### Expected

If I go to the doc index (`.stack-work/install/x86_64-linux/lts-7.0/8.0.1/doc/all/index.html`), I expect to see the executables and test suite dependencies docs.
### Actual

They're not there.
### Stack version

```
$ stack --version
Version 1.2.1, Git revision f28002bdea51468566fd9370f7f9e801c2b51bc5 (4141 commits) x86_64 hpack-0.14.1
```
### Method of installation

Built from git.