cr2: make all imports relative

pylint rightfully complaints about it, so fix it before it becomes a
problem

Change-Id: Iaca7ebc2983d2b4d3871270665fb72558f6a9494
diff --git a/cr2/sched.py b/cr2/sched.py
index 5b2cc28..0a74291 100644
--- a/cr2/sched.py
+++ b/cr2/sched.py
@@ -14,7 +14,7 @@
 # $
 #
 
-from base import Base
+from cr2.base import Base
 from cr2.dynamic import register_dynamic
 from cr2.run import Run