qemu_img_json() is a new helper built on top of qemu_img() that tries to
pull a valid JSON document out of the stdout stream.
In the event that the return code is negative (the program crashed), or
the code is greater than zero and did not produce valid JSON output, the
VerboseProcessError raised by qemu_img() is re-raised.
In the event that the return code is zero but we can't parse valid JSON,
allow the JSON deserialization error to be raised.
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20220321201618.903471-7-jsnow@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>