Copy tools from mounted dir for lxc containers for local provider

Fixes bug: 1357552

Looking at the logs, Juju was unable to curl tools from the http storage server set up for local provider. But only for some containers. This branch makes it so that for lxc containers for local provider, the directory where the tools are built is mounted into the container. The tools URL is patched to point to this location, and thus cloud init performs a file copy rather than an http get.

This is a fix for 1.20 only, since http storage is going away in trunk.

Tested with local provider and also regression tested creating lxc containers on an AWS deployment.
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