vmconfig_apply_pending: add error handling

vmconfig_apply_pending: add error handling

wrap around code which can possibly fail in evals to handle them
gracefully, and log errors.

note: this results in a change of behavior in the API. since errors
are handled gracefully instead of "die"ing, when there is a pending
change which cannot be applied for some reason, it will get logged in
the tasklog but the vm will continue booting regardless. the
non-applied change will stay in the pending section of the
configuration.

Signed-off-by: Oguz Bektas <o.bektas@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>