builders: add cmakebuilder plugin support
The cmakebuilder plugin is used to configure CMake builds to Jenkins,
being able to set several directories and variables related to CMake.
All the possible configurations for the plugin can be set with this
builder. Also included on this change are the documentation and two test
cases, one for common usage types and another more complete.
More information about the plugin can be found at:
Signed-off-by: Lucas Dutra Nunes <email@example.com>