virttest: fix qemu version parsing

[bssrikanth]

Current QEMU_VERSION_RE required parenthetical,
but on custom qemu builds prints only “QEMU emulator version X.Y.Z” on the first line so requirement_checks could not read the version and canceled tests.

This commit fixes it and also adds unittest for the same

[bssrikanth]

I had custom qemu built when queried on version it returned:

#qemu-system-x86_64 --version
QEMU emulator version 10.1.3
Copyright (c) 2003-2025 Fabrice Bellard and the QEMU Project developers

In above case current parsing fails:

[stdlog] 2026-03-25 04:51:40,083 virttest.test_setup.requirement_checks requirement_chec L0057 DEBUG| KVM version: 6.19.4
[stdlog] 2026-03-25 04:51:40,103 virttest.test_setup.requirement_checks requirement_chec L0118 DEBUG| KVM userspace version(qemu): Unknown
[stdlog] 2026-03-25 04:51:40,103 virttest.test_setup.requirement_checks requirement_chec L0124 INFO | Test requires qemu version: [2.12, )
..
[stdlog] 2026-03-25 04:51:40,108 avocado.test stacktrace       L0049 ERROR|   File "/usr/local/lib/python3.12/dist-packages/avocado/core/test.py", line 832, in cancel
[stdlog] 2026-03-25 04:51:40,108 avocado.test stacktrace       L0049 ERROR|     raise exceptions.TestCancel(msg)
[stdlog] 2026-03-25 04:51:40,108 avocado.test stacktrace       L0049 ERROR| avocado.core.exceptions.TestCancel: Can not get host qemu version.

After fix:

..
[stdlog] 2026-03-25 06:02:30,663 virttest.test_setup.requirement_checks requirement_chec L0118 DEBUG| KVM userspace version(qemu): 10.1.3
..

[gemini-code-assist]

Code Review

This pull request updates the QEMU version parsing logic to make the parenthetical build/distro suffix optional, improving compatibility with various version string formats. Changes include regex updates in env_process.py and utils_qemu.py, logic adjustments in requirement_checks.py, and a new unit test. Feedback suggests consolidating the QEMU_VERSION_RE definitions into a single location to reduce code duplication and improve maintainability.

[bssrikanth]

@smitterl @richtja @nickzhq @YongxueHong @zhencliu @cliping @nanli1 @Yingshun @dzhengfy @chloerh @PaulYuuu requesting maintainers review on this pull request.
Thank you for your time in advance.

[harvey0100]

Closing this PR due to current team constraints. This is part of a broader effort to triage all in-flight work across our upstream repos. If this work is still needed, please feel free to reopen and it will be picked up. Apologies for any inconvenience.

[bssrikanth]

This PR as well is fixing a issue in the framework, I would appreciate if this gets reopened.