Support mantisbt and centos better

[marusak]

In mantisbt (pyfaf/bugtrackers/mantisbt.py) there are missing methods clone_bug and create_bug.
In centos (pyfaf/opsys/centos.py) there are missing methods get_component_acls and get_released_builds.

[djuarezg]

Would you consider accepting a PR for this features? I can invest some time on adding these methods.

[ernestask]

Sure, if you need them.

[djuarezg]

I have seen that in the past there were actions related to bug creation. Other BTs such as bugzilla do have these methods. How do these bug creations get triggered? Either I am blind of this action has been removed from the old versions?