[Python] Implement truth testing for lldb.value

[JDevlieghere]

Summary

Python 3 calls bool() instead of len() and lldb.value
only implemented the len method. This adds the bool() implementation.

[davide]

LGTM

lldb/packages/Python/lldbsuite/test/python_api/value/TestValueAPI.py

def test(self):
         self.assertTrue(
             val_s.GetChildMemberWithName('a').AddressOf(),
             VALID_VARIABLE)
         self.assertTrue(
             val_a.Cast(
                 val_i.GetType()).AddressOf(),
             VALID_VARIABLE)
 
+        # Check that lldb.value implements truth testing.
+        self.assertFalse(lldb.value(frame0.FindVariable('bogus')))
+        self.assertTrue(lldb.value(frame0.FindVariable('uinthex')))
+
         self.assertTrue(int(lldb.value(frame0.FindVariable('uinthex')))
                         == 3768803088, 'uinthex == 3768803088')
         self.assertTrue(int(lldb.value(frame0.FindVariable('sinthex')))
                         == -526164208, 'sinthex == -526164208')
 
         self.assertTrue(
             frame0.FindVariable('uinthex').GetValueAsUnsigned() == 3768803088,
             'unsigned uinthex == 3768803088')

lldb/scripts/Python/python-extensions.swig

class value(object):
     print rectangle_array[12]
     print rectangle_array[5].origin.x'''
     def __init__(self, sbvalue):
         self.sbvalue = sbvalue
 
     def __nonzero__(self):
         return self.sbvalue.__nonzero__()
 
+    def __bool__(self):
+        return self.sbvalue.__bool__()
+
     def __str__(self):
         return self.sbvalue.__str__()
 
     def __getitem__(self, key):
         # Allow array access if this value has children...
         if type(key) is value:
             key = int(key)
         if type(key) is int: