Adding the ability to modify cluster templates

- Added function for update cluster template

Change-Id: Ic9f3c685c5d1e43d9d3331abf5bae5e3a932db1d
Implements: blueprint modifying-cluster-template
Adding the ability to modify node group templates

- Added function for update node group template

Implements : blueprint modifying-node-group-template

Change-Id: Ic217885efe8d4098b12bccb01995d77d2f91b5a9
Merge "Adding the ability to modify node group templates"