Switch to packer for configuring cloud infra nodes

Switch to packer for configuring cloud infra nodes

This change switches to packer for building openstack image to be
used by cloud infra nodes on jenkins. It is based on existing script
to setup openstack instances manually and uds packer. [0][1]

In addition to basic configuration, the committed authorized_keys
file can be used for adding user ssh public keys to get them added
into /home/jenkins/.ssh/authorized_keys file via cloud-init script
when the instance boots.

[0] https://gerrit.nordix.org/gitweb?p=infra/tools.git;a=blob;f=infra/jenkins/slave-setup/vm-slave/cloud-infra-slave-setup.sh
[1] https://gerrit.nordix.org/gitweb?p=infra/tools.git;a=tree;f=infra/jenkins/slave-setup/uds-build-server

Change-Id: Ie1932d7098d7c6a0c52206dce785f34076d30881