Basic porter access to the tcpandas

[Michael Hope]

I've added a new job called 'porter' which reserves the first tcpanda
that comes free.  This can be used to reproduce a bug or benchmark
result against an existing binary build.

For example, say you want to see if a fault exists on recent trunk:
 * Go to http://ex.seabright.co.nz/helpers/buildlog/gcc-4.8
 * See the last successful ARM build was gcc-4.8~svn185503
 * Go to http://ex.seabright.co.nz/helpers/scheduler/spawn
 * Spawn a job called 'porter' into the a9-builder queue
 * Keep polling http://ex.seabright.co.nz/helpers/scheduler until a
board shows as 'porter/ready'
 * Log into the board using ssh cbuild at board.v
 * Change to /scratch/cbuild/slave/slaves
 * rsync the binary across using rsync
control:~/cbuild/build/gcc-4.8~svn185503/gcc-*cortexa9*xz .
 * Extract the binary and have at it

The board will drop back into the queue after 48 hours.  You can
release it early by doing a 'killall sleep'.  Please do any work under
/scratch/cbuild/slave/slaves as this is automatically deleted when the
next job starts.

Zhenqiang, could you add this to the jobs page please?

-- Michael