Display the error message on create volume group form
On create volume group form, if the volume type is not selected,
the creation is not successful, but no prompt message is shown.
This patch display error message when volume type is not selected
Closes-Bug:
<noscript><h3>{{ step }}</h3></noscript>
<div class="membership {{ step.slug }}_membership dropdown_fix" data-show-roles="{{ step.show_roles }}">
+ {% include 'horizon/common/_form_errors.html' with form=form %}
<div class="header">
<div class="help_text">{{ step.get_help_text }}</div>
