Add methods to modify the receiver and avoid Marshal.dump/load.
YAML.load produces a new hash, no need to clone it.
Clone the hash once, then call in place modifier methods.
No one calls symbolize directly so don't keep it around.

Unfortunately, MiqDbConfig calls ConfigurationEncoder.stringify, so we can't drop
that yet.
Merge pull request #889 from jrafanie/less_hashy_configuration_encoder

Don't clone so many hashes in ConfigurationEncoder