environs/cloudinit: use actual tools version in bootstrap agent.conf

The upgradedToVersion field in the bootstrap machine agent's config
will now match the tools version that's it's going to use, instead of
the version of the client. This avoids unnecesarily triggering
upgrades at bootstrap time (fixing bug #1358078).
provider/azure: custom data test needs to provide a real tools version

...now that MachineConfig.Tools is used to populate upgradedToVersion
in the initial agent.conf.
Merge pull request #538 from mjs/1358078-avoid-upgrade-with-bootstrap-upload-tools-1.20

environs/cloudinit: use actual tools version in bootstrap agent.conf (1.20 backport)

The upgradedToVersion field in the bootstrap machine agent's config will now match the tools version that's it's going to use, instead of the version of the client. This avoids unnecessarily triggering upgrades at bootstrap time (fixing bug #1358078).

This is the 1.20 backport of https://github.com/juju/juju/pull/535.