support/testing/infra/emulator.py: add qemu version in run log

In some specific situations, there is subtle bugs which depends on a
specific Qemu emulator version and the code it runs.

For example, EDK2 on Aarch64 could work with specific versions of Qemu,
EDK2 and ATF. See commit cc0823c2d "boot/edk2: bump to version
edk2-stable202405" [1].

Also, some Qemu bugs made the guest OS crash. See for example commit
9534b9c00 "package/qemu: fix qemu 9.x issue for AArch32 Secure
PL1&0" [2].

Commit 0d4177598 "support/testing/infra/emulator.py: add build host
dir to qemu search path" added the ability for a runtime test to
select host-qemu in order to use it. It is also possible for a user
to use the "utils/run-tests" script on its host system providing its
own version of Qemu. The Buildroot CI can also use its Qemu version
included in the reference Docker image.

This means the Qemu emulator for running a runtime test can be from
several sources:
- Buildroot Docker reference image,
- Buildroot host-qemu package version,
- Developer host OS qemu version.

Those versions can also change in time.

In order to help debugging of those subtle emulator bugs, this commit
adds a recording of the actual Qemu version used to run a test.

[1] cc0823c2d1
[2] 9534b9c00c
[3] 0d4177598c

Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Romain Naour <romain.naour@smile.fr>

support/testing/infra/emulator.py

@@ -116,15 +116,21 @@ class Emulator(object):
         ldavg_str = f"{ldavg[0]:.2f}, {ldavg[1]:.2f}, {ldavg[2]:.2f}"
         self.logfile.write(f"> host loadavg: {ldavg_str}\n")
         self.logfile.write(f"> timeout multiplier: {self.timeout_multiplier}\n")
-        self.logfile.write("> starting qemu with '%s'\n" % " ".join(qemu_cmd))
+        self.logfile.write(f"> emulator using {qemu_cmd[0]} version:\n")
         host_bin = os.path.join(self.builddir, "host", "bin")
         br_path = host_bin + os.pathsep + os.environ["PATH"]
+        qemu_env = {"QEMU_AUDIO_DRV": "none",
+                    "PATH": br_path}
+        pexpect.run(f"{qemu_cmd[0]} --version",
+                    encoding='utf-8',
+                    logfile=self.logfile,
+                    env=qemu_env)
+        self.logfile.write("> starting qemu with '%s'\n" % " ".join(qemu_cmd))
         self.qemu = pexpect.spawn(qemu_cmd[0], qemu_cmd[1:],
                                   timeout=5 * self.timeout_multiplier,
                                   encoding='utf-8',
                                   codec_errors='replace',
-                                  env={"QEMU_AUDIO_DRV": "none",
-                                       "PATH": br_path})
+                                  env=qemu_env)
         # We want only stdout into the log to avoid double echo
         self.qemu.logfile_read = self.logfile