Add progress indicators to test scripts

The './precommit.sh' tests are starting to take a while, make it easier
to see what's going on by displaying a sort of progress indicator.

e.g.
    gen_doc: . ....... ...OK

In the event of failure, this also makes it easier to tell which of
the steps failed - by counting the pips and comparing to the script.

Test Plan:
$ ./precommit.sh

Determined which static tester was complaining in a particular case, to
look for instructions to ignore the individual instance of the error.
Add 'raw_call()' method to phlsys_conduit

In some cases we want to get the raw response returned from the conduit
API.  Expose a new method on the Conduit class that returns the raw
response and change __call__() to use that.

Test Plan:
$ ./precommit.sh
Exercised in subsequent commits
Add new prototype 'conduit-proxy' command

Make steps towards making it possible to grant limited admin API access
to users, based on custom rules.

Introduce a new prototype command 'conduit-proxy', which serves proxied
conduit via http(s) on a specified port.

Connections to the 'conduit-proxy' go through a trivial auth process
before being forwarded on to the real Phabricator conduit.

Separating the proxy auth process from the Phabricator auth process
means that Phabricator admin credentials may be kept secret.  It also
raises the possibility of introducing customised auth rules.

Teach phlsys_conduit how to connect to the proxy, this means that Arcyon
and Arcyd may use proxies without modification.

Test Plan:
$ ./precommit.sh

Added ./testbed/conduit-proxy/smoketest.sh to exercise the proxy
end-to-end.