merge multi install paths into one

This takes the same approach as the Landscape whereas if
a MAAS server ip and apikey are provided it will do the
MultiInstallWithExistingMaas, otherwise it assumes a new
MAAS install will be performed and continue down that
path.

Signed-off-by: Adam Stokes <adam.stokes@ubuntu.com>
Merge pull request #191 from Ubuntu-Solutions-Engineering/patch-merge-multi-into-one-path

merge multi install paths into one