improve error messages for LXC operations

[cjdcordeiro]

What needs to get done

One of the errors I recently had was about lack of disk space. Only when going in trace verbosity mode I could see:

2024-10-11 13:37:13.303 Executing on host: lxc --project rockcraft copy local:base-instance-rockcraft-buildd-base-v7-c-a38d05774a6de0cf6ab1 local:rockcraft-pro-rock-demo-on-amd64-for-amd64-129341                                                                                                                                              
2024-10-11 13:37:24.008 Failed to copy instance 'local:base-instance-rockcraft-buildd-base-v7-c-a38d05774a6de0cf6ab1' to 'local:rockcraft-pro-rock-demo-on-amd64-for-amd64-129341'.                                                                                                                                                              
2024-10-11 13:37:24.016 Detailed information: * Command that failed: 'lxc --project rockcraft copy local:base-instance-rockcraft-buildd-base-v7-c-a38d05774a6de0cf6ab1 local:rockcraft-pro-rock-demo-on-amd64-for-amd64-129341'
* Command exit code: 1
* Command standard error output: b'Error: Create instance from copy: Failed to run: rsync -a -HA --sparse --devices --delete --checksum --numeric-ids --xattrs --filter=-x security.selinux -q /var/snap/lxd/common/lxd/storage-pools/default/containers/rockcraft_base-instance-rockcraft-buildd-base-v7-c-a38d05774a6de0cf6ab1/ /var/snap/lxd/common/lxd/storage-pools/default/containers/rockcraft_rockcraft-pro-rock-demo-on-amd64-for-amd64-129341: exit status 11 (rsync: write failed on "/var/snap/lxd/common/lxd/storage-pools/default/containers/rockcraft_rockcraft-pro-rock-demo-on-amd64-for-amd64-129341/rootfs/var/lib/snapd/cache/3220c3b05acf2b11b7d0a577ed8b37a103b48c3d9770370f99b770d4653cc2ac45cec2b7f7699cbcdc0b27b239763cb7": No space left on device (28)\nrsync error: error in file IO (code 11) at receiver.c(374) [receiver=3.1.3])\n'                                                                                  

Why it needs to get done

Because Rockcraft's output was not helpful in understanding the root cause:

Starting rockcraft, version 1.5.3.post56+g8f10e0a                                                                                                                       
Logging execution to '/root/.local/state/rockcraft/log/rockcraft-20241011-133648.146458.log'                                                                            
Launching managed ubuntu 22.04 instance...                                                                                                                              
Creating instance from base instance                                                                                                                                    
Failed to copy instance 'local:base-instance-rockcraft-buildd-base-v7-c-a38d05774a6de0cf6ab1' to 'local:rockcraft-pro-rock-demo-on-amd64-for-amd64-129341'.