Re-factoring of LocalSelendroidNode and LocalIOSNode classes. 

Resolution for **"Code refactoring opportunities #48"**:

* In `com.paypal.selion.platform.grid.LocalSelendroidNode` the following methods are being duplicated from `com.paypal.selion.platform.grid.LocalIOSNode`. Hence created an `AbstractNode` from which both `LocalSelendroidNode` and `LocalIOSNode` extend and house these two methods in the abstract class:

    1. `com.paypal.selion.platform.grid.LocalSelendroidNode.waitForNodeToComeUp(int)`
    2. `com.paypal.selion.platform.grid.LocalSelendroidNode.wasNodeSpawned(int)`

* Re-factored `com.paypal.selion.platform.grid.LocalSelendroidNode.startSelendroidDriverNode(int)` to use `org.apache.commons.io.filefilter.FileFilterUtils`