Dolt silently fails to load databases

Dolt silently fails to load databases sometimes, for example permission reasons (example below). I would have preferred `dolt sql` (or anything that starts an engine) to at least warn me about `.dolt` directories that fail to load.

```
maxhoffman@Maxs-MacBook-Pro ~/D/d/tmp2> dolt init
maxhoffman@Maxs-MacBook-Pro ~/D/d/tmp2> dolt sql
# Welcome to the DoltSQL shell.
# Statements must be terminated with ';'.
# "exit" or "quit" (or Ctrl-D) to exit. "/help;" for help.
tmp2/main*> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| tmp2 |
+--------------------+
3 rows in set (0.00 sec)

tmp2/main*> exit
Bye
maxhoffman@Maxs-MacBook-Pro ~/D/d/tmp2> sudo chown -R root .dolt
maxhoffman@Maxs-MacBook-Pro ~/D/d/tmp2> dolt sql
# Welcome to the DoltSQL shell.
# Statements must be terminated with ';'.
# "exit" or "quit" (or Ctrl-D) to exit. "/help;" for help.
> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
+--------------------+
2 rows in set (0.00 sec)

> use tmp2;
database not found: tmp2
```