Update api-parent to use mdsal-binding2-maven-api-gen-plugin instead of maven-sal-api-gen-plugin.

Issues fixed in V2:

• https://jira.opendaylight.org/browse/MDSAL-1 (affects for example ietf-routing model)
• support for non-letter and non-digit enum names, e.g. ‘*’ (verification needed)
• proper YANG 1.1 action support (https://jira.opendaylight.org/browse/MDSAL-299, verification needed), affects mpls models

Possible problems:

• neither netconf nor bgpcep is using binding2, depending on the scope of V2, ODL projects should probably starts using binding2 first (interface incompatibility, bugs, etc.)
• augmentation classes are not generated, instead getters for leaves/containers from augments are generated, e.g.:

interface SimpleContainer {

[...]

java.lang.String getSimpleContainerName();

ComplexAugmentContainer getComplexAugmentContainer();

java.lang.String getSimpleAugmentLeaf();

HC supports writers/readers for augmentation nodes, which will no longer be possible.

This is not a big issue (a matter of typing) in case of augments that add containers.

In case of augments that add just leaves, we don't have information that would allow registering reader/writer for just the leaves from augmentation.

After switching to Binding v2 handler for parent node should also process leaves from augmentations, which introduces some maintainability penalty in case simple augmentation has to be used (model from rfc, etc.).