Description of problem:
The SUI does not allow selecting multiple items in a Service Dialog element with Multiselect enabled.

Version-Release number of selected component (if applicable):
5.8.0

How reproducible:
Always

Steps to Reproduce:
1. Create a Service Dialog with a Dropdown list element and enable the Multiselect option
2. Create a Service Catalog Item that uses the Service Dialog created in step 1
3. Browse to the SUI and order the Catalog Item
4. Select multiple items from the dropdown list

Actual results:
Unable to select multiple items


Expected results:
Able to select multiple items


Additional info:
The multiselect element works as expected in the OPS UI