get-roles command can fail if account has no alias

The regex used to get account information makes the assumption that the account has an alias. Accounts with aliases show up like this:

`Account: {ACCOUNT_ID} ({ALIAS})`

But accounts without aliases show up like this:

`Account: {ACCOUNT_ID}`

At the very least, the regex needs not to cause aws-okta-processor to fail on encountering an account without an alias, but because the alias is baked in to so many other things, the simplest fix might also be to fall back on using the account id as the alias in the event that the account has no alias.