BuildManager: Don't clear the tasklist between init() and run()

Also emit the preamble messages earlier

Change-Id: Iba0308255ba77584e85f52ebc6f422187383ddec
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
CMake: MakeStep: Simplfy code

Change-Id: I4de1ceecc1f0602d0c58ee3e411d43b15437dffb
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>