Add /var and /root free space checks to weka_upgrade_checker

[manmeet-weka]

Summary

• Adds pre-upgrade checks for free space on /var and /root partitions across all backend hosts
• Warns if a partition is less than 20% free; passes if above the threshold
• Reuses a new shared helper free_space_check_path() to avoid duplicating the log-space check logic

Test plan

• Tested against LAB cluster — warnings correctly flagged on hosts with ~6-7% free on both /var and /root
• Verify passes cleanly on a cluster with healthy disk space

🤖 Generated with Claude Code

[vrragosta]

There are a couple of minimal changes that need to accompany every upgrade checker PR:

• Bump the version string in version.txt

• Bump the pg_version in weka_upgrade_checker.py, to match that of version.txt

• Compile the weka_upgrade_checker.py on host 172.29.5.93 -- scp the weka_upgrade_checker.py file to root@172.29.5.93:, ssh into 172.29.5.93 and run the buildit.sh script. Transfer the compiled file, at root@172.29.5.93:~/dist/weka_upgrade_checker to your local branch

Please make these changes and I will continue with a review.

[manmeet-weka]

Done — bumped version to 1.12.2 in both version.txt and pg_version, and updated the compiled binary from 172.29.5.93.

[vrragosta]

I think you want to check the actual root, no? df -m /