Update Interval when timeRemaining is updated

A typical watchdog implementation would give these 2 features:
  - Setting the interval
  - Resetting the timer which also means poke

This watchdog implementation does not provide a poke function
and the same can be achieved by clients making these dbus calls
in that order.

  1) Get the Last set Interval
  2) Set TimeRemaining field to result from #1

To achieve #1, this commit adds the support.

This would make sure that the new timer would expire after last
updated user interval from that time.

Fixes openbmc/openbmc#767

Change-Id: I7393eb32992d7a08518ef463fd0a442df0772392
Signed-off-by: Vishwanatha Subbanna <vishwa@linux.vnet.ibm.com>
diff --git a/test/watchdog_test.cpp b/test/watchdog_test.cpp
index 4e77528..f9a992c 100644
--- a/test/watchdog_test.cpp
+++ b/test/watchdog_test.cpp
@@ -84,6 +84,9 @@
     auto newTime = duration_cast<milliseconds>(expireTime);
     wdog.timeRemaining(newTime.count());
 
+    // Expect an update in the Interval
+    EXPECT_EQ(newTime.count(), wdog.interval());
+
     // Waiting for expiration
     int count = 0;
     while(count < expireTime.count() && !wdog.timerExpired())