[#8844] Testing: Improve instructions and process

[tshradheya]

Fixes #8844

• Fixes IntelliJ cannot run failed tests #8740
• Fixes Tests: certain tests are locale-dependent #8557
• Fixes Firefox: version 46.0.1 causing styling issue #8763
• Fixes StudentProfileAttributesTest: fix instability due to modified timestamp comparison #8871

Outline of Solution

• Made default reported being true so that its standardized for IntelliJ
• Ensured tests are not locale-dependent
• Corrected minor problem in documentation

@LiHaoTan Need input on this #8977 (comment)

NOTE: Continued from #8845 as I messed up the old PR :P

[LiHaoTan]

@tshradheya you haven't addressed the comments: #8977

[tshradheya]

With regard to this: #8977 (comment)

I am not sure how to return a TeammatesDateTimeFormatter and use that for calling the DateTimeFormatter methods by wrapping them

[LiHaoTan]

For example something like this:

public class TeammatesDateTimeFormatter {
    private DateTimeFormatter formatter;

    private TeammatesDateTimeFormatter(DateTimeFormatter formatter) {
        this.formatter = formatter;
    }

    public static TeammatesDateTimeFormatter ofPattern(String pattern) {
        return new TeammatesDateTimeFormatter(DateTimeFormatter.ofPattern(pattern, Locale.US));
    }

    public String format(TemporalAccessor temporal) {
        return formatter.format(temporal);
    }
}