[Docker] Prevent initial run when using cron_schedule

[726a67]

When deployed via docker, podsync performs an initial run and then uses either update_period or cron_schedule to determine when subsequent runs will be performed.

Generally speaking, the purpose of utilizing a cron schedule is to ensure that a given automated process kicks off at a fixed time, date, or interval. In podsync's case, the initial run at least partially undermines the purpose of the cron schedule, since the automated process can be kicked off outside of the defined schedule.

While this isn't a huge issue in and of itself, it can lead to some problematic outcomes, including increased API token usage if the docker container/stack is frequently recreated, and unintended inter-container dependency issues (e.g. podsync attempts to perform a run before a linked vpn container is ready).

One solution to this problem might be to prevent podsync from performing its initial run for feeds where cron_schedule is defined.

Thoughts?