Disable TestXMLDocument.test_xpath which crashes sometimes in CI
Disable TestXMLDocument.test_xpath which crashes sometimes in CI

    Test Case 'TestXMLDocument.test_xpath' started at 2019-03-29 17:27:41.139

    0% tests passed, 1 tests failed out of 1

    Total Test time (real) =  23.90 sec

    The following tests FAILED:
    	  1 - TestFoundation (SEGFAULT)

https://bugs.swift.org/browse/SR-10098

parkera/swift-corelibs-foundation,parkera/swift-corelibs-foundation,parkera/swift-corelibs-foundation,apple/swift-corelibs-foundation,parkera/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,e78l/swift-corelibs-foundation,parkera/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,e78l/swift-corelibs-foundation