cypress: log stdout/stderr when docker exec fails (#9154)
cypress: log stdout/stderr when docker exec fails (#9154)

Otherwise you cannot debug anything with errors like:
```
> Command failed: docker exec 134c9a0afd7dadd0b82ce69b4d72d3d6d8ca1b211540d4390a88357b68fa03b9 pg_isready -U postgres
```
Now we include the stdout/err prior to logging this.
matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk