R1:84f741f40851

Allow config get to work when db is not functional

Summary: Fixes T6554.

Test Plan:
Run `bin/config get mysql.host` when no db is functional. Should not get an exception, but should see:
```
lang=json
{
"config" : [
{
"key" : "mysql.host",
"source" : "local",
"value" : null,
"status" : "unset",
"errorInfo" : null
},
{
"key" : "mysql.host",
"source" : "database",
"value" : null,
"status" : "error"…