Apply pattern matching datasource config files

The Magento\Ui\DataProvider\Config\FileResolver class currently
uses the hardcoded pattern '/*/*/etc/data_source/*' to search
for data source configuration files.
The method argument $filename, which contains the file pattern that should
be matched, is not used.
Due to this temorarily excludng files by renaming them
with a different file type ending is not possible.
For example

    etc/data_source/customer.xml -> etc/data_source/customer.xml.off

This patch applies the specified file name pattern to the pattern.

Author: Vinai

app/code/Magento/Ui/DataProvider/Config/FileResolver.php

@@ -45,7 +45,7 @@ public function get($filename, $scope)
     {
         $iterator = $this->iteratorFactory->create(
             $this->directoryRead,
-            $this->directoryRead->search('/*/*/etc/data_source/*')
+            $this->directoryRead->search('/*/*/etc/data_source/' . $filename)
         );
         return $iterator;
     }

dev/tests/unit/testsuite/Magento/Ui/DataProvider/Config/FileResolverTest.php

@@ -35,10 +35,7 @@ public function setUp()
         $this->fileResolver = new FileResolver($stubFilesystem, $stubFileIteratorFactory);
     }
 
-    /**
-     * @test
-     */
-    public function itShouldApplyTheFilenamePattern()
+    public function testItAppliesTheFilenamePattern()
     {
         $this->mockDirectoryRead->expects($this->once())
             ->method('search')