WIP Fix #3071. Add sql:fetch command

[weitzman]

Per #3071, make it easy to get data out of the Drupal DB in any format.

The command here can be finished easily but the output formatter system has no way to handle variable field input AFAICT. We ran into this limitation once before, I think.

[weitzman]

Arbitrary columns is also needed in migrate-messages command which shows rows with keys of dynamic name and number

[weitzman]

One option that works today - https://stackoverflow.com/questions/39744888/how-to-select-keys-and-values-from-mysql-database-to-a-json-format

[greg-1-anderson]

It's probably a mistake to use RowsOfFields for sql dumps. The library does a lot of processing on the rows, so this would bog down if someone used it to fetch a large database. It's probably better to just return the data as a string and let sql functions such as the one mentioned above do the formatting.

[weitzman]

OK, lets close this with the noted workaround.