[arch] ppc64el maintenance

[sharder996]

A couple fixes for Multipass on ppc64 and s390x:

1. Install cmake from apt as the snap package is no longer being updated. https://forum.snapcraft.io/t/announcement-dropping-architectures-from-the-cmake-snap/35137
2. Edit qemu system arg to use host cpu instead of hardcoded POWER9
3. Filter out non-JSON output from QMP. This was an issue as a ppc64 machine was logging:

May 21 19:38:48 baltar-kernel multipassd[119399]: QMP: Can't open directory /proc/device-tree/cpus/
                                                  Can't open directory /proc/device-tree/cpus/
                                                  Can't open directory /proc/device-tree/cpus/
                                                  {"QMP": {"version": {"qemu": {"micro": 3, "minor": 0, "major": 10}, "package": ""}, "capabilities": ["oob"]}}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.79%. Comparing base (e331c88) to head (5ef3907).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4890      +/-   ##
==========================================
+ Coverage   87.79%   87.79%   +0.01%     
==========================================
  Files         269      269              
  Lines       14636    14641       +5     
==========================================
+ Hits        12848    12853       +5     
  Misses       1788     1788              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.