use --upload-tools when bootstrapping the LXD provider

[Eric Snow]

If you are using the LXD provider, built from the lxd-provider feature
branch, then make sure you use the --upload-tools option when
bootstrapping.

Since the 1.26-alpha1 stream has been released, Juju will download
that instead of the juju you built from the lxd-provider feature
branch.  That means that the machine agent on new instances (e.g. the
new controller) will not know about the LXD provider.  Note that this
is the same as any other provider.  Just a heads up. :)

-eric