TST: skip blosc tests on msgpacks if not installed

Author: Jeff Reback <[email protected]>

Closes #12361 from jreback/blosc and squashes the following commits:

19210d1 [Jeff Reback] TST: skip blosc tests on msgpacks

Author: jreback

pandas/io/tests/test_packers.py

@@ -725,7 +725,11 @@ def read_msgpacks(self, version):
                     f.split('.')[-4][-1] == '2'):
                 continue
             vf = os.path.join(pth, f)
-            self.compare(vf, version)
+            try:
+                self.compare(vf, version)
+            except ImportError:
+                # blosc not installed
+                continue
             n += 1
         assert n > 0, 'Msgpack files are not tested'