*.py: fix incorrect regex escaping (#4961)

Fixes #4959

Author: chitao1234

Diff for: examples/tracing/task_switch.py

@@ -6,7 +6,7 @@
 from time import sleep
 
 b = BPF(src_file="task_switch.c")
-b.attach_kprobe(event_re=r'^finish_task_switch$|^finish_task_switch.isra.d$',
+b.attach_kprobe(event_re=r'^finish_task_switch$|^finish_task_switch\.isra\.\d$',
                 fn_name="count_sched")
 
 # generate many schedule events

Diff for: src/python/bcc/__init__.py

@@ -755,7 +755,7 @@ def get_kprobe_functions(event_re):
                 elif fn.startswith(b'__SCT__'):
                     continue
                 # Exclude all gcc 8's extra .cold functions
-                elif re.match(b'^.*.cold(.d+)?$', fn):
+                elif re.match(br'^.*\.cold(\.\d+)?$', fn):
                     continue
                 if (t.lower() in [b't', b'w']) and re.fullmatch(event_re, fn) \
                     and fn not in blacklist \

Diff for: tests/python/test_trace2.py

@@ -31,7 +31,7 @@ class TestTracingEvent(TestCase):
     def setUp(self):
         b = BPF(text=text, debug=0)
         self.stats = b.get_table(b'stats')
-        b.attach_kprobe(event_re=b'^finish_task_switch$|^finish_task_switch.isra.d$',
+        b.attach_kprobe(event_re=b'^finish_task_switch$|^finish_task_switch\.isra\.\d$',
                         fn_name=b'count_sched')
 
     def test_sched1(self):

Diff for: tools/exitsnoop.py

@@ -204,7 +204,7 @@ def initialize(arg_list = sys.argv[1:]):
         Global.args.timestamp = True
     if not Global.args.ebpf and os.geteuid() != 0:
         return (os.EX_NOPERM, "Need sudo (CAP_SYS_ADMIN) for BPF() system call")
-    if re.match(r'^3.10..*el7.*$', platform.release()): # Centos/Red Hat
+    if re.match(r'^3\.10\..*el7.*$', platform.release()): # Centos/Red Hat
         Global.args.timespec = True
     for _ in range(2):
         c = _embedded_c(Global.args)