Bug 1142178

Description of problem:
No error messages output if append '--format qcow2' after '-a guest.img', but if i put '--format qcow2' before '-a guest.img', virt-customize will detect the image format and print a error.


Version-Release number of selected component (if applicable):
libguestfs-1.27.43-1.1.el7


How reproducible:
100%


Steps to Reproduce:
1. Create a raw format guest image: rhel6.6.img
2. #virt-customize  --hostname unused -a rhel6.6.img --format qcow2
[   0.0] Examining the guest ...
[   5.0] Setting a random seed
[   5.0] Setting the hostname: unused
[   5.0] Finishing off

3. virt-customize  --format qcow2 --hostname unused -a rhel6.6.img
[   0.0] Examining the guest ...
virt-customize: error: libguestfs error: could not create appliance through
libvirt.

Try running qemu directly without libvirt using this environment variable:
export LIBGUESTFS_BACKEND=direct

Original error from libvirt: internal error: process exited while
connecting to monitor: Warning: option deprecated, use lost_tick_policy
property of kvm-pit instead.
qemu-kvm: -drive
file=/root/rhel6.6.img,if=none,id=drive-scsi0-0-0-0,format=qcow2,cache=writeback,discard=unmap:
could not open disk image /root/rhel6.6.img: Image is not in qcow2 format
 [code=1 domain=10]

If reporting bugs, run virt-customize with debugging enabled and include
the complete output:

  virt-customize -v -x [...]


Actual results:
Step 2 have no message output, it seems virt-customize use auto-detection model even though you append '--format qcow2' at the end of the command line.

Expected results:
Step 2 have a error message output, because you specify '--format qcow2', but guest.img is a raw format file

Additional info: