automation: Enhance pytest header

Mention NetworkManager RPM and Operating System in pytest header.
Example:

```
================= test session starts ==================
[...]
RPMs: NetworkManager-1.20.5-1.cab2e4fc96.el8.x86_64
OS: CentOS Linux 8 (Core)
```

This makes it easier to identify the test environment from the pytest
log. For example when the tests are running on bare-metal or in a VM
instead of the container that is setup with run-tests.sh.

Signed-off-by: Till Maas <opensource@till.name>

tests/integration/conftest.py

@@ -18,6 +18,7 @@
 #
 
 import logging
+import subprocess
 
 import pytest
 
@@ -26,6 +27,11 @@ import libnmstate
 from .testlib import ifacelib
 
 
+REPORT_HEADER = """RPMs: {rpms}
+OS: {osname}
+"""
+
+
 @pytest.fixture(scope='session', autouse=True)
 def logging_setup():
     logging.basicConfig(
@@ -61,3 +67,23 @@ def preserve_old_config():
     old_state = libnmstate.show()
     yield
     libnmstate.apply(old_state, verify_change=False)
+
+
+def pytest_report_header(config):
+    return REPORT_HEADER.format(
+        rpms=_get_package_nvr('NetworkManager'), osname=_get_osname()
+    )
+
+
+def _get_package_nvr(package):
+    return (
+        subprocess.check_output(['rpm', '-q', package]).strip().decode('utf-8')
+    )
+
+
+def _get_osname():
+    with open('/etc/os-release') as os_release:
+        for line in os_release.readlines():
+            if line.startswith('PRETTY_NAME='):
+                return line.split('=', maxsplit=1)[1].strip().strip('"')
+    return ''