RFR: JDK-8024849 Don't remove upper case letters from username when setting USER_RELEASE_SUFFIX

[Magnus Ihse Bursie]

When creating USER_RELEASE_SUFFIX, the username is processed to only 
include "safe" characters. Unfortunately, upper case letters are 
stripped out even though they at a later stage is supposed to be 
converted to lower case.

Also fix typo in comment.

Webrev:
http://cr.openjdk.java.net/~ihse/JDK-8024849-allow-upper-case-for-username-in-USER_RELEASE_SUFFIX/webrev.01

/Magnus