Update CHANGELOG
provisoner/salt-masterless: lowercase package name

/cc @rgarcia - I don't know of any Go packages that follow this naming
convention so I just lowercased it.
plugin/provisioner-salt-masterless: add empty test file

/cc @rgarcia - This just forces the tests to make sure the package
even builds. Better than nothing.
plugin/provisioner-salt-masterless: compile again
provisioner/salt-masterless: use common lib for config decoding

/cc @rgarcia - Since you opened the pull request, common config
decoding stuff has been pulled out into the common Package. This
simplifies a lot of code.
provisioner/salt-masterless: don't capitalize Ui

/cc @rgarcia - Not sure why this was capitalized to begin with
provisioner/salt-masterless: use Messages for minor steps

/cc @rgarcia - "Message" in Ui is the non-bold colored messages and
are meant for sub-messages or steps part of a larger message. "Say"
is used for the bold stuff. This is more in line wit how Packer works.
provisioner/salt-masterless: verify local_state_tree exists

/cc @rgarcia