PyTest.summaryf: better detection of summary line

If program output after pytest's summary line, our summary function
would be confused and detect 0 test run.
Make this matching more robust by expecting the actual status of tests
reported by pytest: (x)passed, (x)failed, skipped errors or "no test run"

From Kirill's suggestion on nexedi/nxdtest!17 (comment 162070)

nxdtest/__init__.py

@@ -499,7 +499,7 @@ class PyTest:
         # ...
         textv = out.splitlines()
         for l in reversed(textv):
-            if re.match(b'^====* .* ====*$', l):
+            if re.match(rb'^====* .*(failed|passed|skipped|error|no tests).* ====*$', l):
                 pytail = l
                 break
         else:

nxdtest/nxdtest_pytest_test.py

@@ -131,6 +131,46 @@ golang/time_test.py:106: AssertionError
 b(''),
 'fail\ttestname\t1.000s\t# 112t 0e 1f 13s')
 
+case1('notest', b("""\
+============================= test session starts ==============================
+platform linux -- Python 3.7.7, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
+rootdir: /srv/slapgrid/slappart15/srv/runner/software/104d3d67a7dca200da22b97280c85eb6/parts/nxdtest, inifile: pytest.ini
+plugins: timeout-1.4.2, mock-2.0.0
+collected 0 items
+
+========================= no tests ran in 0.01 seconds =========================
+"""),
+b(''),
+'ok\ttestname\t1.000s\t# 0t 0e 0f 0s')
+
+case1('error', b("""\
+============================= test session starts ==============================
+platform linux -- Python 3.7.7, pytest-4.6.11, py-1.9.0, pluggy-0.13.1
+rootdir: /srv/slapgrid/slappart15/srv/runner/software/104d3d67a7dca200da22b97280c85eb6/parts/nxdtest, inifile: pytest.ini
+plugins: timeout-1.4.2, mock-2.0.0
+collected 0 items / 2 errors                                                   
+
+==================================== ERRORS ====================================
+_________________________ ERROR collecting tmp/test.py _________________________
+ImportError while importing test module 'tmp/test.py'.
+Hint: make sure your test modules/packages have valid Python names.
+Traceback:
+test.py:4: in <module>
+    import error
+E   ModuleNotFoundError: No module named 'error'
+________________________ ERROR collecting tmp/test2.py _________________________
+ImportError while importing test module 'tmp/test2.py'.
+Hint: make sure your test modules/packages have valid Python names.
+Traceback:
+test2.py:4: in <module>
+    import error
+E   ModuleNotFoundError: No module named 'error'
+!!!!!!!!!!!!!!!!!!! Interrupted: 2 errors during collection !!!!!!!!!!!!!!!!!!!!
+=========================== 2 error in 0.11 seconds ============================
+"""),
+b(''),
+'error\ttestname\t1.000s\t# 2t 2e 0f 0s')
+
 case1('ok+tailtext', b("""\
 date:   Sun, 08 Nov 2020 12:26:24 MSK
 xnode:  kirr@deco.navytux.spb.ru
@@ -146,6 +186,7 @@ wcfs: 2020/11/08 12:26:38 /tmp/testdb_fs.Z9IvT0/1.fs: watcher: stat /tmp/testdb_
 # unmount/stop wcfs pid39653 @ /tmp/wcfs/40cc7154ed758d6a867205e79e320c1d3b56458d
 wcfs: 2020/11/08 12:26:38 /tmp/testdb_fs.B3rbby/1.fs: watcher: stat /tmp/testdb_fs.B3rbby/1.fs: use of closed file
 # unmount/stop wcfs pid39595 @ /tmp/wcfs/d0b5d036a2cce47fe73003cf2d9f0b22c7043817
+==== aaa bbb ====
 """),
 b(''),
 'ok\ttestname\t1.000s\t# 55t 0e 0f 0s')