Test for unset job node_bitmap as the job may not yet be scheduled

Work still needed on scheduling, launch, env vars, etc.
This just creates the job records

-v for every pack job component combined in first pass of parsing

Still need to document the API, flesh out slurmctld response and
  more work on sbatch logic

Make _opt_default() function in salloc and sbatch reetrant.
Re-initializing variables used to hold changable fields for
each component of the heterogeneous job.

Document the new pack job APIs slurm_allocate_pack_job_blocking()
  and slurm_pack_job_lookup().

Used the wrong variable name in one place

No change in logic

Also minor logic changes for env vars

This sets most env vars, but not all

Operations performed on pack leader are applied to all components
  of the heterogeneous job.
Requests to operate on any other heterogeneous job component returns
  an error.

Remove logic that was intended for temporary use while debugging
  commit d763675c

Moved logic so it could be used for both pack job and normal job

This is the equivalent to slurm_allocation_lookup() for pack jobs.

This will insure the backfill scheduler starts as soon as possible
  after the pack jobs become eligible to run

No change in functionality in this commit

If job_complete call is issued against the pack leader then mark
  entire pack job as complete. This is used by salloc/srun on
  termination.

No change in functionality, just refactor the logic for re-use.

Just in case something goes wrong with the test, this should clear
  the job relatively soon

The RESPONSE_JOB_PACK_ALLOCATION RPC returns a list of
  RESPONSE_RESOURCE_ALLOCATION data types. Error handling
  still needs to be added to slurmctld/agent.c, blocking
  for resources does not work yet, and the salloc code
  does not handle the List response type yet.

Expect seems to be sometimes truncating the output from "salloc --help"
  resulting in a test failure. This is a bug in Expect not Slurm. Modified
  the test to not parse all the way to the end of the expected output so
  the test always passes.

No change in logic

No change in logic yet, but added a function to determine if there
  are pending pack job components and moved the data structure
  build logic to a separate function so it can be called for
  each pack job component

Use syntax "scancel #+#". For example "scancel 1+2" cancels component
 number 2 from job 1