Milo: Add machine pool info for buildbot builder view.

milo/api/resp/botstatus_string.go

+// Code generated by "stringer -type=BotStatus"; DO NOT EDIT.
+
+package resp
+
+import "fmt"
+
+const _BotStatus_name = "UnknownStatusIdleBusyDisconnected"
+
+var _BotStatus_index = [...]uint8{0, 13, 17, 21, 33}
+
+func (i BotStatus) String() string {
+        if i < 0 || i >= BotStatus(len(_BotStatus_index)-1) {
+                return fmt.Sprintf("BotStatus(%d)", i)
+        }
+        return _BotStatus_name[_BotStatus_index[i]:_BotStatus_index[i+1]]
+}