Add OutputAnalyzer(Path) constructor

This is useful for looking for patterns in logging files that can grow quite large.
This is taken from code from

    /**
     * Verify that the contents of the file contains the given the set of strings
     *
     * @param file File to check for expectedStrings
     * @param expectedStrings Strings that file should contain
     * @throws RuntimeException If the string was not found
     * @throws IOException If the file cannot be opened
     */
    public OutputAnalyzer shouldContain(File file, String ... expectedStrings) throws IOException {