cmdline: add collect-logs subcommand.

Add a new collect-logs sub command to the cloud-init CLI. This script
will collect all logs pertinent to a cloud-init run and store them in a
compressed tar-gzipped file. This tarfile can be attached to any
cloud-init bug filed in order to aid in bug triage and resolution.

A cloudinit.apport module is also added that allows apport interaction.
Here is an example bug filed via ubuntu-bug cloud-init: LP: #1716975.

Once the apport launcher is packaged in cloud-init, bugs can be filed
against cloud-init with the following command:
  ubuntu-bug cloud-init

LP: #1607345