health: Flusing disk's buffer before benchmark
health: Flusing disk's buffer before benchmark

Prior any fio benchmarking, let's flush disk's cache to avoid any
performance issue.

As the run_fio() function is called many time, let's be sure that no
more data are located in disk's cache before starting.

That might not be handled by some Raid controller.

enovance/edeploy,redhat-cip/edeploy,lebauce/edeploy,lebauce/edeploy,redhat-cip/edeploy,redhat-cip/edeploy,enovance/edeploy,redhat-cip/edeploy,lebauce/edeploy,enovance/edeploy,lebauce/edeploy,enovance/edeploy