[Alarm] Fix failures raised from test suite.

I've downloaded the test suite from http://otcqa.sh.intel.com/qa-auto/live/Web_TCT_Xwalk/ and run them manually.
All the alarm related failures in the test suite have been fixed.

BUG=XWALK-2163
This purpose is to ensure the attribute "date" **readonly**.
In the constructor, I store the input argument `date` in the local variable `local_date` and bind it with the getter of the attribute "date".
The `get: function() {return new Date();}` returns current time however I want it to return the original value, e.g. `get: function() {return new Date(local_date);}`.  Other readonly objects have the similar logic.

This change is based on the test case `AlarmAbsolute_date_attribute.html`:

    date = new Date();     // now
    alarm = new tizen.AlarmAbsolute(date);
    tmp = alarm.date.getTime();
    alarm.date.setSeconds(50, 0);
    assert_equals(tmp, alarm.date.getTime(), "date can be modified");