Harmonize build/initialize's interpretation of the PWD

[aaaaalbert]

Reviewing @heatherm's PR SeattleTestbed/docs#39 shows that build.py and initialize.py treat their PWD and suggested target paths inconsistently. For example, running ../../repy_v2/build.py will use the correct paths to copy files from, though expecting its target dir inside the PWD at call time. OTOH, initialize.py requires its config file in the PWD.

We should clean this up and make initialize.py and build.py independent of the PWDand adopt a common understanding of where the target path is supposed to be located. This perhaps requires a doc change as well.

Proposed overall workflow:

$ cd COMPONENT
$ mkir TARGET_DIR
$ python scripts/initialize.py
$ python scripts/build.py TARGET_DIR

[aaaaalbert]

Concretely, this piece in initialize should do what this piece in build_component does.