Add a suggestion for non-English locale of Linux in the test doc

[Jing Tian]

Hi,

We have discussed the issue of the test cases fail because of locale 
before[1].

Thanks for the suggestions given by Naoto and David. I think we can put 
this advice in the test doc, which may be better for people to test. 
This advice can avoid the problem that caused by locale and we can pay 
more attention to the functional points that the test itself focuses on.

Set JTREG="VM_OPTIONS=-Duser.language=en -Duser.country=US" , it does 
pass most test cases, but there are still very few test cases(7 in 
total) can't pass the test when they are in a non-English locale.

I think if 'make test' in a non-English locale, we can set the locale to 
English first. Use 'export LANG="en_US"'. But this method is just for 
Linux. I test "tier1 tier2 tier3" after setting LANG="en_US". The 
problems caused by the local settings have not appeared anymore.


JBS: https://bugs.openjdk.java.net/browse/JDK-8222444
Webrev: http://cr.openjdk.java.net/~lzhai/8222444/webrev.00/

The testing.html is updated automatically using "make update-build-docs" 
with pandoc version 2.7.2.

[1] 
https://mail.openjdk.java.net/pipermail/compiler-dev/2019-March/013144.html 
<https://mail.openjdk.java.net/pipermail/compiler-dev/2019-March/013144.html>

Cheers,
Jing Tian