Fix incorrect raising of database_does_not_exist error
When we're raising the error with the args list [1], the
format for the args is a list of arguments not a single arg. So the previous
invocations of `erlang:error(database_does_not_exist, ?b2l(Id))` would produce
a args list of individual database name characters [2].
[1] https://www.erlang.org/doc/man/erlang#error-2
[2] > mem3_shards:opts_for_db(<<"doesnotexit">>).
```
** exception error: database_does_not_exist
in function mem3_shards:opts_for_db/11
called as mem3_shards:opts_for_db(100,111,101,115,110,111,116,101,120,105,116)
```
4 files changed
