Arcyd: refactor, extract abdi_processrepos

Move the logic of processing repositories out of abdcmd_processrepos and
into a new module so that it can be shared with the new 'arcyd start'
command.

Test Plan:
$ ./precommit.sh
Arcyd: fix repo paths for dashboard

Fix the parsing of the repo configs during 'arcyd start' to match the
expected input for 'arcyd process-repos'.

Fix the paths to the '.ok' and '.try' files to match the expected by the
reporter and dashboard code. In later work we'll want to make the
reporter and dashboard re-use the same code so the paths are identical.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
$ ./testbed/arcyd/test_shell.sh

Conflicts:
	py/abd/abdcmd_start.py
Arcyd: move root config file to 'configfile'

Change the path of the root config file to 'configfile' to make way for
a 'config' directory.  Update abdcmd_start to get the name of the config
file from abdt_fs instead of hard-coding it.

Test Plan:
$ ./precommit.sh
Arcyd: move config files to new 'config' dir

Tidy the root directory by making a new directory hierarchy for
configuration files, separating 'phabricator' from 'repository'.

Simplify abdcmd_start by moving the config file discovery logic out to
abdt_fs.

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
$ ./testbed/arcyd/test_shell.sh