Format tests.xml and result.xml by `xmllint --format`

Reference: http://xmlsoft.org/xmllint.html
This just formats the .xml files' indent with 2 spaces, empty line.
`tests.xml` and `result.xml` look the same as before.

Expect the generated result.xml use 2 spaces indent.
Merge pull request #48 from zqzhang/zqzhang/xml-format

Format tests.xml and result.xml by `xmllint --format`