[server][FaceRest] Support to monitor "New Value Per Second"

In this implementation, NVPS is calculated when items are fetched,
then they are stored into 'servers' table.
FaceRest just returns stored the value of nvps.
[server][FaceRest] Return error immediately during retriving the value of nvps
[server][testFaceRest] Add test for the value of nvps
Merge branch 'support-new-values-per-second-on-dashboard' of github.com:kenhys/hatohol into kenhys-support-new-values-per-second-on-dashboard

Conflicts:
	server/test/testFaceRest.cc