exit code is 0 when converge plan has errors

[ryane]

If running converge plan results in errors, the exit code from the process should be zon-zero:

$ ./converge plan --local samples/fileMode.hcl
2016-11-10T13:38:01-05:00 |INFO| serving        addr=:47740 component=rpc
2016-11-10T13:38:01-05:00 |WARN| skipping module verification   component=client
2016-11-10T13:38:01-05:00 |INFO| got status     component=client file=samples/fileMode.hcl id=root/param.filename run=STARTED stage=PLAN
2016-11-10T13:38:01-05:00 |INFO| got status     component=client file=samples/fileMode.hcl id=root/file.mode.render run=STARTED stage=PLAN
2016-11-10T13:38:01-05:00 |INFO| got status     component=client file=samples/fileMode.hcl id=root/task.query.hostname run=STARTED stage=PLAN
2016-11-10T13:38:01-05:00 |INFO| got status     component=client file=samples/fileMode.hcl id=root run=STARTED stage=PLAN

root/task.query.hostname:
 Error: error in dependency "root/file.mode.render"
 Messages:
 Has Changes: yes
 Changes: No changes

root/file.mode.render:
 Error: cannot set mode for file that does not exist
 Messages:
  "test.txt" does not exist
 Has Changes: yes
 Changes:
  test.txt: "----------" => "-r-x--x--x"

Summary: 3 errors, 3 changes

 * root/file.mode.render: cannot set mode for file that does not exist
 * root/task.query.hostname: error in dependency "root/file.mode.render"
 * root: error in dependency "root/task.query.hostname"

$ echo $?
0