feat!: add Python 3.8, drop Python 3.3

[tswast]

Updates OpenPGP Public Keys based on fingerprints published at
https://www.python.org/downloads/ Double-checked locally via

docker build -t python-multi ./python/googleapis/python-multi > log.txt

and

grep -C 3 fingerprint log.txt

Output:

$ grep -C 4 fingerprint log.txt
gpg:                 aka "Benjamin Peterson"
gpg:                 aka "Benjamin Peterson"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: C01E 1CAD 5EA2 C4F0 B8E3  5715 04C3 67C2 18AD D4FF
+ rm -r /tmp/tmp.eCQGdKJjRC python-2.7.17.tar.xz.asc
+ mkdir -p /usr/src/python-2.7.17
+ tar -xJC /usr/src/python-2.7.17 --strip-components=1 -f python-2.7.17.tar.xz
+ rm python-2.7.17.tar.xz
--
--
gpg: Signature made Mon Mar 18 17:16:22 2019 UTC using RSA key ID F73C700D
gpg: Good signature from "Larry Hastings"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: 97FC 712E 4C02 4BBE A48A  61ED 3A5C A953 F73C 700D
+ rm -r /tmp/tmp.WTl4FqLzKE python-3.4.10.tar.xz.asc
+ mkdir -p /usr/src/python-3.4.10
+ tar -xJC /usr/src/python-3.4.10 --strip-components=1 -f python-3.4.10.tar.xz
+ rm python-3.4.10.tar.xz
--
--
gpg: Signature made Fri Nov  1 23:34:18 2019 UTC using RSA key ID F73C700D
gpg: Good signature from "Larry Hastings"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: 97FC 712E 4C02 4BBE A48A  61ED 3A5C A953 F73C 700D
+ rm -r /tmp/tmp.sr7jZA9T08 python-3.5.9.tar.xz.asc
+ mkdir -p /usr/src/python-3.5.9
+ tar -xJC /usr/src/python-3.5.9 --strip-components=1 -f python-3.5.9.tar.xz
+ rm python-3.5.9.tar.xz
--
--
gpg:                 aka "keybase.io/nad"
gpg:                 aka "Ned Deily (Python release signing key)"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: 0D96 DF4D 4110 E5C4 3FBF  B17F 2D34 7EA6 AA65 421D
+ rm -r /tmp/tmp.hyrEvHaBki python-3.6.9.tar.xz.asc
+ mkdir -p /usr/src/python-3.6.9
+ tar -xJC /usr/src/python-3.6.9 --strip-components=1 -f python-3.6.9.tar.xz
+ rm python-3.6.9.tar.xz
--
--
gpg:                 aka "keybase.io/nad"
gpg:                 aka "Ned Deily (Python release signing key)"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: 0D96 DF4D 4110 E5C4 3FBF  B17F 2D34 7EA6 AA65 421D
+ rm -r /tmp/tmp.z9yXq0MOWn python-3.7.5.tar.xz.asc
+ mkdir -p /usr/src/python-3.7.5
+ tar -xJC /usr/src/python-3.7.5 --strip-components=1 -f python-3.7.5.tar.xz
+ rm python-3.7.5.tar.xz
--
--
gpg:                 aka "Łukasz Langa (Work e-mail account)"
gpg:                 aka "[jpeg image of size 24479]"
gpg: WARNING: This key is not certified with a trusted signature!
gpg:          There is no indication that the signature belongs to the owner.
Primary key fingerprint: E3FF 2839 C048 B25C 084D  EBE9 B269 95E3 1025 0568
+ rm -r /tmp/tmp.urDxkVrtYt python-3.8.0.tar.xz.asc
+ mkdir -p /usr/src/python-3.8.0
+ tar -xJC /usr/src/python-3.8.0 --strip-components=1 -f python-3.8.0.tar.xz
+ rm python-3.8.0.tar.xz

Closes #42

[busunkim96]

Job to rebuild images: https://fusion.corp.google.com/projectanalysis/summary/KOKORO/prod%3Acloud-devrel%2Fclient-libraries%2Ftesting-infra-docker%2Frelease%2Fpython?search_pattern=testing-infra-docker&include_inactive_projects=false