- split out usernameLength and displaynameLength truncation values,
as they are different things
- fetch username and displayname lengths from the role, not from
the request parameters
- add appropriate defaults for username and displayname lengths
If a single token generates multiple myself roles, the generated mysql
username was previously prepended with the displayname of the vault
user; this makes the output of `show processlist` in mysql potentially
difficult to correlate with the roles actually in use without cross-
checking against the vault audit log.
See https://github.com/hashicorp/vault/pull/1603 for further discussion.
1) Use the new LeaseExtend
2) Use default values controlled by mount tuning/system defaults instead
of a random hard coded value
3) Remove grace periods
