[test][bionic] Force python3 and utf-8 encoding

bionic's /usr/bin/python is python2. Encoding and python2/python3 is.... complicated.
Those tests already run on py3 which is the default for Ubuntu Focal and Fedora 34.

This change symlinks /usr/local/bin/python to python3 within the Bionic container
and changes all tools to use "#!/usr/bin/env python" shebang instead of "#!/usr/bin/python"
which allows to use the default python set by the environment.

To add insult to injury. Python 3.6 still needs a bit of help to default to UTF-8
which can be achieved with the env var `PYTHONIOENCODING` to `utf-8`.
Since python 3.7, [UTF-8 mode is enabled by default when the locale is C or POSIX](https://docs.python.org/3/whatsnew/3.7.html#whatsnew37-pep540).
Some more details about this problem can be found here: https://vstinner.github.io/posix-locale.html#misconfigured-locales-in-docker-images

Illustration:
```
root@bionic:/# locale
LANG=
LANGUAGE=
LC_CTYPE="POSIX"
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=
root@bionic:/# python2
Python 2.7.17 (default, Jul  1 2022, 15:56:32)
[GCC 7.5.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> print("%s" % u'\xb7')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character u'\xb7' in position 0: ordinal not in range(128)
>>>
root@bionic:/# python3
Python 3.6.9 (default, Jun 29 2022, 11:45:57)
[GCC 8.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print("%s" % u'\xb7')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeEncodeError: 'ascii' codec can't encode character '\xb7' in position 0: ordinal not in range(128)
>>>
root@bionic:/# PYTHONIOENCODING=utf-8 python3
Python 3.6.9 (default, Jun 29 2022, 11:45:57)
[GCC 8.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print("%s" % u'\xb7')
·
```

On Focal:
```
root@focal:/# locale
LANG=
LANGUAGE=
LC_CTYPE="POSIX"
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=
root@focal:/# python3
Python 3.8.10 (default, Jun 22 2022, 20:18:18)
[GCC 9.4.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> print("%s" % u'\xb7')
·
```

Author: chantra

docker/Dockerfile.tests

@@ -72,3 +72,4 @@ RUN wget -O ruby-install-0.7.0.tar.gz \
 
 RUN ruby-install --system ruby 2.6.0 -- --enable-dtrace
 RUN if [ ! -f "/usr/bin/python" ]; then ln -s /bin/python3 /usr/bin/python; fi
+RUN if [ ! -f "/usr/local/bin/python" ]; then ln -s /usr/bin/python3 /usr/local/bin/python; fi

tests/wrapper.sh.in

@@ -9,6 +9,7 @@ kind=$1; shift
 cmd=$1; shift
 
 PYTHONPATH=@CMAKE_BINARY_DIR@/src/python/bcc-python3
+PYTHONIOENCODING=utf-8
 LD_LIBRARY_PATH=@CMAKE_BINARY_DIR@:@CMAKE_BINARY_DIR@/src/cc
 
 ns=$name
@@ -32,15 +33,15 @@ function ns_run() {
   sudo ip netns exec $ns ethtool -K eth0 tx off
   sudo ip addr add dev $ns.out 172.16.1.1/24
   sudo ip link set $ns.out up
-  sudo --preserve-env=PYTHON_TEST_LOGFILE env PYTHONPATH=$PYTHONPATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH ip netns exec $ns $cmd "$@"
+  sudo --preserve-env=PYTHON_TEST_LOGFILE env PYTHONIOENCODING=$PYTHONIOENCODING PYTHONPATH=$PYTHONPATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH ip netns exec $ns $cmd "$@"
   return $?
 }
 function sudo_run() {
-  sudo --preserve-env=PYTHON_TEST_LOGFILE env PYTHONPATH=$PYTHONPATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH $cmd "$@"
+  sudo --preserve-env=PYTHON_TEST_LOGFILE env PYTHONIOENCODING=$PYTHONIOENCODING PYTHONPATH=$PYTHONPATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH $cmd "$@"
   return $?
 }
 function simple_run() {
-  PYTHONPATH=$PYTHONPATH PYTHON_TEST_LOGFILE=$PYTHON_TEST_LOGFILE LD_LIBRARY_PATH=$LD_LIBRARY_PATH $cmd "$@"
+  PYTHONIOENCODING=$PYTHONIOENCODING PYTHONPATH=$PYTHONPATH PYTHON_TEST_LOGFILE=$PYTHON_TEST_LOGFILE LD_LIBRARY_PATH=$LD_LIBRARY_PATH $cmd "$@"
   return $?
 }