Get the postgres console output code from restore_sql

[gaborcsardi]

For a table that exists:

root@r-pkg:~# echo "select NULL foo from daily LIMIT 1" | dokku psql:restore_sql cranlogs
 foo 
-----

(1 row)

root@r-pkg:~# echo $?
0

For a table that does not exist:

root@r-pkg:~# echo "select NULL foo from foobar LIMIT 1" | dokku psql:restore_sql cranlogs
ERROR:  relation "foobar" does not exist
LINE 1: select NULL foo from foobar LIMIT 1
                             ^
root@r-pkg:~# echo $?
0

It would be useful to check if the query finished properly. I could also try to parse the output, but it would be simpler to just return the exit code of psql.