(PUP-1881) Correct Windows runinterval behavior

Previously when Puppet parsed a runinterval of 0 on Windows, it would
set the runinterval to 1800 seconds, Puppet's default runinterval value.
This was incorrect behavior, as on other platforms and in the
documentation, a runinterval of 0 indicates that Puppet should run
continuously.

This commit updates the Windows daemon to set the runinterval to 1800
seconds when it receives an empty string and cast to integer in all
other cases.

ext/windows/service/daemon.rb

@@ -161,10 +161,13 @@ def report_windows_event(type, id, message)
   # @return runinterval [Integer] How often to do a Puppet run, in seconds.
   def parse_runinterval(puppet_path)
     begin
-      runinterval = %x(#{puppet_path} config --section agent --log_level notice print runinterval).to_i
-      if runinterval == 0
+      runinterval = %x(#{puppet_path} config --section agent --log_level notice print runinterval).chomp
+      if runinterval == ''
         runinterval = 1800
         log_err("Failed to determine runinterval, defaulting to #{runinterval} seconds")
+      else
+        # Use Kernel#Integer because to_i will return 0 with non-numeric strings.
+        runinterval = Integer(runinterval)
       end
     rescue Exception => e
       log_exception(e)