How do I convince Erlang's Common Test to spawn local nodes?

Question

I'd like to have Common Test spin up some local nodes to run suites. To that end, I've got the following spec file:

{node, a, 'a@localhost'}.

{logdir, [a,master], "../logs/"}.

{init, [a], [{node_start, [{callback_module, slave}
                           %% , {erl_flags, "-pa ../ebin/"}                                                                                                    
                           %% , {monitor_master, true}                                                                                                         
                          ]}]}.

{suites, [a], "." , all}.

Which works okay:

> erl -sname ct@localhost
Erlang R15B03 (erts-5.9.3) [source] [64-bit] [smp:8:8] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.9.3  (abort with ^G)
(ct@localhost)1> ct_master:run("itest/lk.spec").
=== Master Logdir ===
/Users/blt/projects/us/troutwine/locker/logs
=== Master Logger process started ===
<0.41.0>
Node a@localhost started successfully with callback slave
=== Cookie ===
'DJWDEGHCXBKRAYVPMHTX'
=== Starting Tests ===
Tests starting on: [a@localhost]
=== Test Info ===
Starting test(s) on a@localhost...

********** node_ctrl process <6888.38.0> started on a@localhost **********

Common Test starting (cwd is /Users/blt/projects/us/troutwine/locker)


Common Test: Running make in test directories...
Including the following directories:
[]

CWD set to: "/Users/blt/projects/us/troutwine/locker/logs/[email protected]_09.44.23"

TEST INFO: 1 test(s), 1 suite(s)

Testing locker.itest: Starting test (with repeated test cases)

- - - - - - - - - - - - - - - - - - - - - - - - - -
locker_SUITE:init_per_suite failed
Reason: {badmatch,{error,{"no such file or directory","locker.app"}}}
- - - - - - - - - - - - - - - - - - - - - - - - - -

Testing locker.itest: *** FAILED *** init_per_suite
Testing locker.itest: TEST COMPLETE, 0 ok, 0 failed, 100 skipped of 100 test cases

Updating /Users/blt/projects/us/troutwine/locker/logs/index.html... done
Updating /Users/blt/projects/us/troutwine/locker/logs/all_runs.html... done
=== Test Info ===
Test(s) on node a@localhost finished.
=== TEST RESULTS ===
a@localhost_____________________________{0,0,{0,100}}

=== Info ===
Updating log files
=== Info ===

[{"itest/lk.spec",ok}]

without, obviously, running any tests on the extra local node. Now, when I uncomment the extra configuration in the spec so that it looks like

{init, [a], [{node_start, [{callback_module, slave}
                           , {erl_flags, "-pa ../ebin/"}                                                                                                    
                           , {monitor_master, true}                                                                                                         
                          ]}]}.

the result is less than what I'd hoped for:

(ct@localhost)2> ct_master:run("itest/lk.spec").
=== Master Logdir ===
/Users/blt/projects/us/troutwine/locker/logs
=== Master Logger process started ===
<0.41.0>

=ERROR REPORT==== 7-Aug-2013::11:05:24 ===
Error in process <0.51.0> on node 'ct@localhost' with exit value: {badarg,[{erlang,open_port,[{spawn,[101,114,108,32,45,100,101,116,97,99,104,101,100,32,45,110,111,105,110,112,117,116,32,45,109,97,115,116,101,114,32,99,116,64,108,111,99,97,108,104,111,115,116,32,32,45,115,110,97,109,101,32,97,64,108,111,99,97,108,104,111,115,116,32,45,115,32,115,108,97,118,101,32,115,108,97,118,101,95,115,116,97,114,116,32,99,116,64,108,111,99,97,108,104,111,115,116,32,115,108,97,118,101,95,119,97,105,116,101,114,95,48,32,{erl_flags,"-pa ../ebin/"},{monitor_master,true}]},[stream... 

Am I doing anything obviously wrong here?