Fix ObjCDataFormatterTestCase.test_nsdate_* tests

The time/date strings (like "6pm April 10, 1985") are interpreted as a local time but CFDateGetAbsoluteTime() returns time in UTC. It caused a problem when local time was UTC+0100 or more (0200, 0300 etc.):
```
======================================================================
FAIL: test_nsdate_with_dsym_and_run_command (TestDataFormatterObjC.ObjCDataFormatterTestCase)
    Test formatters for NSDate.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/IliaK/p/llvm/tools/lldb/test/lldbtest.py", line 462, in wrapper
    return func(self, *args, **kwargs)
  File "/Users/IliaK/p/llvm/tools/lldb/test/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjC.py", line 157, in test_nsdate_with_dsym_and_run_command
    self.appkit_tester_impl(self.buildDsym,self.nsdate_data_formatter_commands)
  File "/Users/IliaK/p/llvm/tools/lldb/test/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjC.py", line 34, in appkit_tester_impl
    commands()
  File "/Users/IliaK/p/llvm/tools/lldb/test/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjC.py", line 475, in nsdate_data_formatter_commands
    substrs = ['1985-04','2011-01'])
  File "/Users/IliaK/p/llvm/tools/lldb/test/lldbtest.py", line 2146, in expect
    msg if msg else EXP_MSG(str, exe))
AssertionError: False is not True : '2011-01' returns expected result
Config=x86_64-clang
======================================================================
FAIL: test_nsdate_with_dwarf_and_run_command (TestDataFormatterObjC.ObjCDataFormatterTestCase)
    Test formatters for NSDate.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/IliaK/p/llvm/tools/lldb/test/lldbtest.py", line 479, in wrapper
    return func(self, *args, **kwargs)
  File "/Users/IliaK/p/llvm/tools/lldb/test/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjC.py", line 163, in test_nsdate_with_dwarf_and_run_command
    self.appkit_tester_impl(self.buildDwarf,self.nsdate_data_formatter_commands)
  File "/Users/IliaK/p/llvm/tools/lldb/test/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjC.py", line 34, in appkit_tester_impl
    commands()
  File "/Users/IliaK/p/llvm/tools/lldb/test/functionalities/data-formatter/data-formatter-objc/TestDataFormatterObjC.py", line 475, in nsdate_data_formatter_commands
    substrs = ['1985-04','2011-01'])
  File "/Users/IliaK/p/llvm/tools/lldb/test/lldbtest.py", line 2146, in expect
    msg if msg else EXP_MSG(str, exe))
AssertionError: False is not True : '2011-01' returns expected result
Config=x86_64-clang
```

llvm-svn: 232946