Allow to run Makefile for another directory

[marckhouzam]

It is possible for a user to run make from outside of the acceptance-testing directory. For example

$ cd /tmp $ make -f $GOPATH/src/helm.sh/acceptance-testing/Makefile

To support this, the Makefile must use the ROOT_DIR of where the Makefile resides, so as to find all other files.

Signed-off-by: Marc Khouzam [email protected]