RunFactories: Simplify pathFromId by using Core::Id::suffixAfter

Change-Id: I2b65071be3e57c59588e6421d15c7739c257e1c5
Reviewed-by: Daniel Teske <daniel.teske@digia.com>
Allow the user to restrict rc creation to certain .pro

Task-number: QTCREATORBUG-10953
Change-Id: Iff1a31c007ac777bfa390d48237480ef56ffc0e4
Reviewed-by: Eike Ziller <eike.ziller@digia.com>