Capability requirement on jobs shoud be set automatically when Nunit runner task is added

When an Nunit task is added to a job, Bamboo should automatically add a requirement that the executable for NUNIT must exist similar to what is achieved when adding tasks such as the MSBUILD. This will avoid users from having to manually configure the requirements. Again there are cases where the lack of this will cause builds to fail because the wrong agents (Linux OS agents) for example attempt to pick the build from queue