Added better error handling when a DB driver is wrong defined (fix #10)

[daria-lewandowska]

Fixes #10
Summary of changes:
-better error handling

Testing done:
-integration test

[marcin-krolik]

Consider moving json content as separate file and read it

[daria-lewandowska]

done

[marcin-krolik]

There is still incorrectly handled error in closeDBs()

[daria-lewandowska]

I'm not sure how should I handle this error in closeDBs(),
you think it will be ok to do:
return fmt.Errorf("Cannot close connection to database %+s\n", dbs[i].DBName)
instead of:
fmt.Fprintf(os.Stdout, "Cannot close connection to database %+v, err=%+v\n", dbs[i].DBName, err)

[marcin-krolik]

@daria-lewandowska yes, I'd suggest to add error as returned type to closeDBS() function, but would not return early from loop. I think you should try to close all existing DB connections, and if any fails, return an error

[marcin-krolik]

LGTM