Issues with test runner configuration

https://github.com/haskell/hackage-server/blob/1217eb00fd1f0fb9b37dd45e600d143250841cd0/exes/BuildClient.hs#L654-L666

IMO there are a few issues with this:

* Hiding `--test-show-details` is very unhelpful. Presumably users are supposed to access `--test-log` somehow, but I cannot find any link to it in UI.
* Why `--disable-optimizations`? This breaks inspection testing (fusion rules and such), here is an example: https://github.com/haskell/text/issues/634
* `--enable-coverage` [prevents test execution](https://hackage.haskell.org/package/reflex-dom-core-0.8.1.4/reports/1) for any package depending on `vector` (so pretty much any non-trivial package) because of
```
Resolving dependencies...
Error:
Internal libraries only supported with per-component builds.
Per-component builds were disabled because program coverage is enabled
In the package 'vector-0.13.2.0'
```