[LNT] Python 3 support: adapt csv reader open

Summary:
csv.reader have different expectation between Python versions regarding
the file object it reads from. On Python 2 it requires the file to have
been opened in binary mode while on Python 3 it requires text mode and
universal newlines mode enabled but forwarded untranslated to the
caller. This commit use an if to cater to both requirements.

Reviewers: cmatthews, hubert.reinterpretcast, kristof.beyls, leandron, PrzemekWirkus

Reviewed By: PrzemekWirkus

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D68800

Author: Thomas Preud'homme

lnt/tests/nt.py

@@ -771,7 +771,10 @@ def append_to_sample_keys(tup):
             append_to_sample_keys((True, 'jit.exec', 'JIT', 'time'))
 
     # Load the report file.
-    report_file = open(report_path, 'rb')
+    if sys.version_info[0] < 3:
+        report_file = open(report_path, 'rb')
+    else:
+        report_file = open(report_path, 'r', newline='')
     reader_it = iter(csv.reader(report_file))
 
     # Get the header.