core: Introducing runInternalXXX at CommandBase

This patch addds runInternalXXX methods to CommandBase, and changes
ivocation of Backend.getInstance().runInternalXXX where possible

This will give the following benefits:

1. Less code
2. Will add the ability to introduce (during inheritence for example) specific
treatment to runInternalXXX
if needed
3. Ease of mocking

Change-Id: Ia7f3a3283836325eca72f9db3cc3115861a2d555
Signed-off-by: Yair Zaslavsky <yzaslavs@redhat.com>