Updated stansummary to not quit on non-fatal error (#971)

[bbbales2]

Submisison Checklist

• Run tests: ./runCmdStanTests.py src/test
• Declare copyright holder and open-source license: see below

Summary:

Fix for #971

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company): Columbia University

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[mitzimorris]

LGTM!

[stan-buildbot]

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Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	3.43	3.46	0.99	-0.87% slower
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	0.93	-7.13% slower
eight_schools/eight_schools.stan	0.11	0.11	1.02	2.13% faster
gp_regr/gp_regr.stan	0.15	0.15	1.0	-0.04% slower
irt_2pl/irt_2pl.stan	5.23	5.22	1.0	0.27% faster
performance.compilation	92.38	90.11	1.03	2.46% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	8.66	8.67	1.0	-0.06% slower
pkpd/one_comp_mm_elim_abs.stan	28.95	28.33	1.02	2.12% faster
sir/sir.stan	136.9	130.48	1.05	4.69% faster
gp_regr/gen_gp_data.stan	0.04	0.04	0.97	-2.65% slower
low_dim_gauss_mix/low_dim_gauss_mix.stan	3.05	3.12	0.98	-2.51% slower
pkpd/sim_one_comp_mm_elim_abs.stan	0.4	0.39	1.03	2.47% faster
arK/arK.stan	1.82	1.82	1.0	-0.46% slower
arma/arma.stan	0.61	0.6	1.02	2.11% faster
garch/garch.stan	0.59	0.6	0.99	-0.52% slower
Mean result: 1.00206573872

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Jenkins Console Log
Blue Ocean
Commit hash: 761b108

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Machine information

ProductName: Mac OS X ProductVersion: 10.11.6 BuildVersion: 15G22010

CPU:
Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

G++:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

Clang:
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix