Improve consistency of *.cbuild[-idx].yml nodes

**Describe the bug**
*.cbuild-idx.yml has the following nodes:
```
build-idx:
  csolution: solution.csolution.yml
  cprojects:
```
while *.cbuild.yml:
```
build:
  solution: ../../../../solution.csolution.yml
  project: ../../../../project/project.cproject.yml
```

The use of prefix `c` should be consistently defined across the several possible yaml nodes. 