THRIFT-3515 Python 2.6 compatibility and test on CI

This closes #766
diff --git a/lib/py/src/protocol/TCompactProtocol.py b/lib/py/src/protocol/TCompactProtocol.py
index a8b025a..6023066 100644
--- a/lib/py/src/protocol/TCompactProtocol.py
+++ b/lib/py/src/protocol/TCompactProtocol.py
@@ -56,7 +56,7 @@
 
 
 def writeVarint(trans, n):
-  out = []
+  out = bytearray()
   while True:
     if n & ~0x7f == 0:
       out.append(n)
@@ -64,7 +64,7 @@
     else:
       out.append((n & 0xff) | 0x80)
       n = n >> 7
-  trans.write(bytearray(out))
+  trans.write(bytes(out))
 
 
 def readVarint(trans):