sim: track changes in flux-core to jansson functions

[SteVwonder]

Tracks changes in flux-framework/flux-core#1104

Old	New
flux_kvs_lookup_getf()	flux_kvs_lookup_get_unpack()
flux_msg_set_jsonf()	flux_msg_pack()
flux_msg_vset_jsonf()	flux_msg_vpack()
flux_msg_get_jsonf()	flux_msg_unpack()
flux_msg_vget_jsonf()	flux_msg_vunpack()
flux_rpcf()	flux_rpc_pack()
flux_rpc_getf()	flux_rpc_get_unpack()
flux_event_decodef()	flux_event_unpack()
flux_event_encodef()	flux_event_pack()
flux_request_decodef()	flux_request_unpack()
flux_respondf()	flux_respond_pack()

Fixes #254

[SteVwonder]

I am getting runtime error messages from the simulator, but the tests pass.
Example error message:

2017-07-19T21:04:14.879698Z sim_exec.err[0]: pull_job_from_kvs: failed to get starting_time in lwj.0.0.1: No such file or directory

I'm tracking down those errors now. We can merge this PR and I'll submit another PR for those errors, or we can wait until I fix those errors. I'm fine with either.

[coveralls]

Coverage remained the same at 73.735% when pulling aa511ed on SteVwonder:track-core-changes into 9f77522 on flux-framework:master.

[codecov-io]

Codecov Report

Merging #255 into master will not change coverage.
The diff coverage is 90.9%.

@@          Coverage Diff           @@
##           master    #255   +/-   ##
======================================
  Coverage    69.9%   69.9%           
======================================
  Files          25      25           
  Lines        5286    5286           
======================================
  Hits         3695    3695           
  Misses       1591    1591

Impacted Files	Coverage Δ
simulator/simsrv.c	72.9% <100%> (ø)	⬆️
simulator/submitsrv.c	84.09% <100%> (ø)	⬆️
simulator/simulator.c	83.76% <85.71%> (ø)	⬆️

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[garlick]

Looks great @SteVwonder. I'll go ahead and merge since travis passed and this is just name changes.