Fixed double slash issue

OBS arm builds fail with this error:
/usr/lib/rpm/debugedit: canonicalization unexpectedly shrank by one
character

The root cause of this was empty VPATH variable in Makefile. For example
-I ./$(VPATH)/d becomes -I .//d and causes this build failure if VPATH
is empty

This commit is fixing this issue by removing VPATH from src/Makefile.am
May be it would be better to assign VPATH=. by default

Change-Id: I8bb3120d2eba163e23b7f5aff033c859000f50b2
Signed-off-by: Ed Bartosh <eduard.bartosh@intel.com>
Version bump, development version 0.7-0.rc0
Merging OBS arm build fix
AAL/Python: fixed returning None from adapter log bug

If the adapter block returns None, it's considered as a successful
execution of the adapter code.