ESO query functions - order retrieved table columns as in the list passed to the function

## Version 0.4.12.dev10525

```
>>> import astroquery as aq
>>> aq.__version__
'0.4.12.dev10525'
```

## Observed behavior:

The columns of the retrieved table are not ordered as in the list provided by the user.

```
>>> from astroquery.eso import Eso
>>> eso = Eso()
>>> eso.query_main(columns = ['dp_id', 'dec', 'ra' ])[:0]

ra dec dp_id
deg deg
float64 float64 object
------- ------- ------
```

## Expected behavior:

The columns of the retrieved table are ordered as in the list provided by the user.

```
>>> from astroquery.eso import Eso
>>> eso = Eso()
>>> eso.query_main(columns = ['dp_id', 'dec', 'ra' ])[:0]

dp_id dec ra
deg deg
object float64 float64
------ ------- -------
```

## How to reproduce:

... see snippets above. This happens for all ESO functions `query_*(...)`.

Start with the astroquery.eso.Eso query_main and the other query_* entry points described in the issue, then reproduce the column-order difference with the provided Python snippets. Done means every ESO query function returns columns in the same order as the user's columns list.

Written by the indexing model from the issue text.