updater: Add Commmand class to manage BBOTA commands.

Move the commands map parsing out of PerformBlockImageUpdate(), as this
can be done more easily by the caller.

The goal (not done in this CL) is to decouple command parsing logic from
the performers. This allows (a) focusing on the command logic in the
performer; and (b) extending BBOTA commands syntax separately.

Test: Run recovery_unit_test and recovery_component_test.
Change-Id: Ife202398a7660b152d84a3ba17b90f93d19c55f2
diff --git a/tests/Android.mk b/tests/Android.mk
index 853ca27..ff42066 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -37,6 +37,7 @@
 
 LOCAL_SRC_FILES := \
     unit/asn1_decoder_test.cpp \
+    unit/commands_test.cpp \
     unit/dirutil_test.cpp \
     unit/locale_test.cpp \
     unit/rangeset_test.cpp \