Disable tests that use the internet

Plist DTDs were recently moved from
http://www.apple.com/DTDs/PropertyList-1.0.dtd to
https://www.apple.com/DTDs/PropertyList-1.0.dtd (note the https).
libXML, however, is not setup to request DTDs from secure domains and
fails.  This causes a spurious failure in the validation test checking
for failure and a real failure in the validation test checking for
success.  In either case, these tests introduce a hard dependency on
the internet into the test suite.  I’ve disabled them for now and filed
rdar://31567922 about this.

Author: CodaFi

TestFoundation/TestNSXMLDocument.swift

@@ -289,6 +289,8 @@ class TestNSXMLDocument : XCTestCase {
         XCTAssertEqual(element.localName, "root")
     }
 
+    /*
+     * <rdar://31567922> Re-enable these tests in a way that does not depend on the internet.
     func test_validation_success() throws {
         let validString = "<?xml version=\"1.0\" standalone=\"yes\"?><!DOCTYPE foo [ <!ELEMENT foo (#PCDATA)> ]><foo>Hello world</foo>"
         do {
@@ -330,7 +332,7 @@ class TestNSXMLDocument : XCTestCase {
         } catch let error as NSError {
             XCTAssert((error.userInfo[NSLocalizedDescriptionKey] as! String).contains("Element true was declared EMPTY this one has content"))
         }
-    }
+    }*/
 
     func test_dtd() throws {
         let node = XMLNode.dtdNode(withXMLString:"<!ELEMENT foo (#PCDATA)>") as! XMLDTDNode