psu: Add code to get pollInterval from JSON file

Add in a helper function to open JSON file and parse out the configuration
properties. Use the helper function to get the pollInterval in the constructor.

Signed-off-by: Brandon Wyman <bjwyman@gmail.com>
Change-Id: Ia8cf1c148a1685e2e09703c02e469a0bff034af5
diff --git a/phosphor-power-supply/main.cpp b/phosphor-power-supply/main.cpp
index 2622c6a..03ff3db 100644
--- a/phosphor-power-supply/main.cpp
+++ b/phosphor-power-supply/main.cpp
@@ -22,7 +22,7 @@
 
 #include <filesystem>
 
-using namespace phosphor::power::manager;
+using namespace phosphor::power;
 
 int main(int argc, char* argv[])
 {
@@ -57,9 +57,7 @@
         // handle both sd_events (for the timers) and dbus signals.
         bus.attach_event(event.get(), SD_EVENT_PRIORITY_NORMAL);
 
-        // TODO: Should get polling interval from JSON file.
-        auto pollInterval = std::chrono::milliseconds(1000);
-        PSUManager manager(bus, event, pollInterval);
+        manager::PSUManager manager(bus, event, configfile);
 
         return manager.run();
     }