This commit adds a new option --prefix to "role grant-permission"
command. If the option is passed, the command interprets the key as a
prefix of range permission.
Example of usage:
$ ETCDCTL_API=3 bin/etcdctl --user root:p role grant-permission --prefix r1 readwrite /dir/
Role r1 updated
$ ETCDCTL_API=3 bin/etcdctl --user root:p role get r1
Role r1
KV Read:
[/dir/, /dir0)
[k1, k5)
KV Write:
[/dir/, /dir0)
[k1, k5)
$ ETCDCTL_API=3 bin/etcdctl --user u1:p put /dir/key val
OK