functional tests: only send sector-aligned IO

... to satisfy OCF assumptions.

Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>

tests/functional/pyocf/types/data.py

@@ -107,7 +107,13 @@ class Data:
 
     @classmethod
     def from_string(cls, source: str, encoding: str = "ascii"):
-        return cls.from_bytes(bytes(source, encoding))
+        b = bytes(source, encoding)
+        # duplicate string to fill space up to sector boundary
+        padding_len = S.from_B(len(b), sector_aligned = True).B - len(b)
+        padding = b * (padding_len // len(b) + 1)
+        padding = padding[:padding_len]
+        b = b + padding
+        return cls.from_bytes(b)
 
     @staticmethod
     @DataOps.ALLOC