csv output option

Would be good to have a *csv* output option, so that we could easily extract fields using good old linux cli commands and without redoing any formatting of any kind.

Like in the example below the first field has space in it.

```
$ az account list-locations -o table
DisplayName Latitude Longitude Name
-------------------- ---------- ----------- ------------------
East Asia 22.267 114.188 eastasia
Southeast Asia 1.283 103.833 southeastasia
Central US 41.5908 -93.6208 centralus
East US 37.3719 -79.8164 eastus
East US 2 36.6681 -78.3889 eastus2
West US 37.783 -122.417 westus
```

Would be good to have this:
```
$ az account list-locations -o csv
East Asia,22.267,114.188,eastasia
Southeast Asia,1.283,103.833,southeastasia
Central US,41.5908,-93.6208,centralus
East US,37.3719,-79.8164,eastus
East US,2,36.6681,-78.3889,eastus2
West US,37.783,-122.417,westus
North Central US,41.8819,-87.6278,northcentralus
South Central US,29.4167,-98.5,southcentralus
```
So we can do things like this:
```
$ az account list-locations -o csv | awk -F, '{ print $4" -> "$1 }'
eastasia -> East Asia
southeastasia -> Southeast Asia
centralus -> Central US
eastus -> East US
eastus2 -> East US 2
westus -> West US
```

I think this option could come handy sometimes.