phlsys_tryloop: add default delay factories

Make the tryloop easier to use by adding some helpers to create default
delays.  Add confidence by exercising the delay generators so they can
be depended on in rarely-run circumstances.

Test Plan: $ ./precommit.sh
Conduit: allow conduits to describe themselves

Also, make phlsys_conduit.Conduit a new-style class so properties work.

Test Plan: $ ./precommit.sh
Arcyd: refactor tryloops in 'processrepos'

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
break git in $ ./testbed/arcyd/test_shell.sh
Arcyd: tryloops on branch.land operations

Test Plan:
$ ./precommit.sh
$ ./testbed/arcyd/acceptance_tests.sh
Arcyd: retry loop around marking new review as ok

In case the remote Git repository intermittently fails, retry the
operation a few times after a short delay.

This will greatly reduce the disruption caused by an unreliable
service but not eliminate it.

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