mcf: Correct typos in error messages

Correct spelling and grammar mistakes in several error messages.

Open-webOS-DCO-1.0-Signed-off-by: Susan Montooth <susan.montooth@palm.com>
Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>
gitignore: Split build products section and move pycache there

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>
mcf: Don't checkout while cloning layers

* git checkout is called later with specified BRANCH and COMMIT
  parameters
* git clone even with -n creates HEAD branch (usually master).
  Call git checkout with -B to ignore existing branches.
  Fixes "fatal: A branch named 'master' already exists."
  when branch=master is used in submission parameter.

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>