Fix error callback issue in pool modification

When the user submit a pool modification with duplicate name
or reduced pg count,rest-api returns the validation error.
But the corresponding error callback is not getting called and
the form doesn't show the errors.

The issue is due to the interception of rest-api response to
change code 304 to code 200 and not properly handling other status
codes. This is now fixed by properly transmitting the errors.

Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>
show pool validation errors on the form

While creating/updating a pool,if the server
throws any validation errors for the parameters sent
on the request, the errors will be shown near
to the respective field itself.

In case the error is not specific to any of the fields,
then it will be shown in a popup.

Fixes: #7480
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>
Merge pull request #51 from kmkanagaraj/fix-pool-form

show pool validation errors on the form