RFR: 8280357: user.home = "?" when running with systemd DynamicUser=true [v2]

[Roger Riggs]

> In some Linux configurations, the Linux home directory provided by getpwent is not usable.
> The value of the system property `user.home` should fallback to the value of $HOME 
> if getpwent.user_home is null or less that 2 characters long. "/" is not a valid home directory name.
> 
> If $HOME is undefined or empty, the value of the getpwent.user_home is retained.
> 
> There are more details in the Jira issue: https://bugs.openjdk.java.net/browse/JDK-8280357
> 
> The fix has been tested manually on Ubuntu 20.0.4 using the suggested systemd command line and variations.

Roger Riggs has updated the pull request incrementally with one additional commit since the last revision:

  fallback to '?' for user.home if both the pw_dir and /Users/rriggs are not valid

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7534/files
  - new: https://git.openjdk.java.net/jdk/pull/7534/files/d67d2c44..ad7c0287

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7534&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7534&range=00-01

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7534.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7534/head:pull/7534

PR: https://git.openjdk.java.net/jdk/pull/7534