Add an EnvironmentFile directive to read in a configuration file with environment variables. The "-" prefix means it can proceed if the file doesn't exist.
This would allow users to keep sensitive information like the SUPERUSER/REPLICATION passwords in the config file separate from a YAML file that might be deployed from source control.
* Update the startup script shutdown / startup timeout to allow the current sync node time to release the role in synchronous_mode.
Without this change Patroni will be killed while waiting, and will leave
PostgreSQL up rather than stopping it.
* Updates to support strict sync mode.
If synchronous_mode_strict==true then 'patroni_dummy_host' will be written as synchronous_standby_names
when that last replication host dies.
* Oops, mixed two pull requests - backing out one
