Add FileUploader form element XSD definition

I'm not sure if the solution proposed in this commit is correct, but I
couldn't figure out any more logical way to deal with the validation
errors on the Travis CI build. The error follows:

1) Magento\Test\Integrity\Xml\SchemaTest::testXmlFiles Passed: 1881,
Failed: 6, Incomplete: 0, Skipped: 0.  Data set:
/app/code/Magento/Catalog/view/adminhtml/ui_component/category_form.xml
Error validating
/home/travis/build/magento/magento2/app/code/Magento/Catalog/view/adminhtml/ui_component/category_form.xml
against urn:magento:module:Magento_Ui:etc/ui_configuration.xsd
Array (
[0] => Element 'fileUploader': This element is not expected. Expected is
one of ( hidden, file, input, date, boolean, checkbox, checkboxset,
email, select, multiselect ).  Line: 168
[1] => Element 'wysiwyg',
attribute 'class': The attribute 'class' is not allowed.  Line: 206
)
Failed asserting that an array is empty.

Element zero in that array is what I am attempting to fix here.

Author: neillrobson

app/code/Magento/Ui/etc/ui_configuration.xsd

@@ -226,6 +226,7 @@
             <xs:element name="price" type="formElementPrice" maxOccurs="unbounded"/>
             <xs:element name="radioset" type="formElementRadioset" maxOccurs="unbounded"/>
             <xs:element name="wysiwyg" type="formElementWysiwyg" maxOccurs="unbounded"/>
+            <xs:element name="fileUploader" type="formElementFileUploader" maxOccurs="unbounded"/>
         </xs:choice>
     </xs:group>
 

app/code/Magento/Ui/view/base/ui_component/etc/definition/fileUploader.xsd

@@ -23,6 +23,19 @@
         <xs:attributeGroup ref="ui_element_attributes"/>
     </xs:complexType>
 
+    <xs:complexType name="formElementFileUploader">
+        <xs:sequence>
+            <xs:element name="settings" minOccurs="0" maxOccurs="1">
+                <xs:complexType>
+                    <xs:choice minOccurs="0" maxOccurs="unbounded">
+                        <xs:group ref="componentFileUploaderSettings"/>
+                    </xs:choice>
+                </xs:complexType>
+            </xs:element>
+        </xs:sequence>
+        <xs:attributeGroup ref="ui_element_attributes"/>
+    </xs:complexType>
+
     <xs:group name="componentFileUploaderSettings">
         <xs:choice>
             <xs:group ref="abstractSettings"/>