Description of problem:
drive_add does not use a common prefix for errors, thus making errors like:
"LUKS version 2 is not supported\r\n" hard to parse
Steps to Reproduce:
1. Create a LUKSv2 disk
2. Try attaching it via libvirt
"LUKS version 2 is not supported\r\n"
"Error: LUKS version 2 is not supported\r\n"
There was an error prefix added upstream:
HMP: Prepend errors with 'Error:'
but drive_add does not seem to be using hmp_handle_error
as of upstream commit 185b7ccc11354cbd69b6d53bf8d831dd964f6c88
At this point libvirt already uses blockdev-add, which has error reporting by default, so there's no point in fixing the HMP version.