title: Quartz properties file pass in environment variables
body: <p>I'm trying to add environment variables to my quartz properties file, but it's not being loaded properly.</p>
  
  <p>Heres my quartz.properties</p>
  
  <pre><code>  org.quartz.scheduler.instanceName: scheduler
    org.quartz.scheduler.instanceId: AUTO
    org.quartz.scheduler.skipUpdateCheck: true
    org.quartz.threadPool.class: org.quartz.simpl.SimpleThreadPool
    org.quartz.threadPool.threadCount: 10
    org.quartz.threadPool.threadPriority: 5
    org.quartz.jobStore.misfireThreshold: 60000
    org.quartz.jobStore.class: org.quartz.impl.jdbcjobstore.JobStoreTX
    org.quartz.jobStore.driverDelegateClass: org.quartz.impl.jdbcjobstore.PostgreSQLDelegate
    org.quartz.jobStore.useProperties: false
    org.quartz.jobStore.dataSource: myDS
    org.quartz.jobStore.tablePrefix: QRTZ_
    org.quartz.jobStore.isClustered: true
    org.quartz.dataSource.myDS.driver: org.postgresql.Driver
    org.quartz.dataSource.myDS.URL: ${APP_JDBC_URL:-jdbc:postgresql://localhost:5432/db}
    org.quartz.dataSource.myDS.user:  ${APP_JDBC_USER:-user}
    org.quartz.dataSource.myDS.password: ${APP_JDBC_PASSWORD:-pass}
    org.quartz.dataSource.myDS.maxConnections: 5
    org.quartz.dataSource.myDS.validationQuery: select 1
  </code></pre>
  
  <p>Exception:</p>
  
  <pre><code>ERROR [2018-03-13 21:11:13,958] org.quartz.impl.jdbcjobstore.JobStoreTX: ClusterManager: Error managing cluster: Failed to obtain DB connection from data source 'myDS': java.sql.SQLException: Connections could not be acquired from the underlying database!
  ! com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.
  ! at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1319)
  ! at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:557)
  ! at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477)
  ! at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)
  ! ... 26 common frames omitted
  </code></pre>