Update jenkins build slave packer script
In this change,
- Packer image build scripts updated with below entries in order to fix an issue
with Let's Encrypt certificate when cloning repo from gerrit.est.tech due to DST
Root CA X3 Expiration: https://letsencrypt.org/docs/dst-root-ca-x3-expiration-september-2021/
1. Remove outdated certificate from system:
# rm -rf /usr/share/ca-certificates/mozilla/DST_Root_CA_X3.crt
2. Update CA certificates on the system
# sudo update-ca-certificates --fresh --verbose
Change-Id: I7a0eebe0e3ea6b7624b89e090cac566bca47e401