Refactor AES operations to generalize block cipher operations.

In preparation for adding 3DES support, this CL moves the code that
does all the block cipher work from AesOperation to
EvpBlockCipherOperation (and associated classes).  To make it easier
to see what was changed, the block cipher code was left in
aes_operation.{cpp|h}.  The next CL will move it to separate files.

Test: make (local unit tests), CTS & VTS
Change-Id: Ibbf870c351425ea8d990218aa0ae089d0b2ada4b
diff --git a/.gitignore b/.gitignore
index 8c7799b..ab162f3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -5,6 +5,6 @@
 *.run
 *.memcheck
 *.massif
-/*_test
+/tests/*_test
 /coverage.info
 /coverage/