tarmac.conf: keep branch cache in uniform location.

This will make it slightly easier to run the tarmac lander as an
arbitrary user. Only two changes to tarmac-lander.conf and a slight
variation in the instructionsa re needed. These changes (and a new need
to create/chown the branch cache directory) were added to the README
file.
added first stab at charming deployment
FOREVER ALONE: I have no relations :(
create global tarmac branch dir
temporary change to use my configs without disturbing tarmac
temporary change to use my configs without disturbing tarmac
a TODO - fix git on existing