fix: make sure to fail rather than continue if rsync fails

[joshtrichards]

Ran across an in-the-wild environment where rsync was failing due to I/O disk errors, but initializing continued on anyhow. We should check the exit values and fail hard since it'll result in a broken installation (and may get overlooked until later depending on what files the errors occur on).

2025-01-13T15:13:04.250546270Z Initializing nextcloud 30.0.4.1 ...
2025-01-13T15:13:13.543136088Z rsync: [sender] read errors mapping "/usr/src/nextcloud/apps/text/js/pgsql-6nMyK_Wd.chunk.mjs.map": I/O error (5)
[...]
2025-01-13T15:13:13.791311797Z ERROR: apps/text/js/pgsql-6nMyK_Wd.chunk.mjs.map failed verification -- update discarded.
[...]
2025-01-13T15:13:18.615971825Z rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1338) [sender=3.3.0]
2025-01-13T15:13:18.903862977Z Initializing finished
2025-01-13T15:13:18.903916218Z New Nextcloud instance.
2025-01-13T15:13:18.913472340Z Installing with pgsql database
2025-01-13T15:13:18.913679471Z Starting Nextcloud installation...

Follow-up ideas:

• wrap in a function
• create a generic "run_this()` function that checks exit values for any commands

P.S. Should probably get more testing.

[joshtrichards]

@szaimen FYI - This turned up (on the forum) with an AIO user and both images share similar rsync code in the entrypoint:

https://github.com/nextcloud/all-in-one/blob/c1f1207a0e1cc1e70a0620e4be70d0a2129cc907/Containers/nextcloud/entrypoint.sh#L220