Don't print the whole stack trace on Connection error.

[matriv]

It now looks like that:

➭ bin/crash -v --verify-ssl true --cert-file /tmp/certs/marios.crt --key-file /tmp/certs/marios.key --ca-cert-file /tmp/certs/rootCA.crt --hosts https://127.0.0.1:4200 -U unknonwn
/Users/matriv/crate/crash/eggs/urllib3-1.14-py3.6.egg/urllib3/connection.py:266: SubjectAltNameWarning: Certificate for 127.0.0.1 has no `subjectAltName`, falling back to check for a `commonName` for now. This feature is being removed by major browsers and deprecated by RFC 2818. (See https://github.com/shazow/urllib3/issues/497 for details.)`
  SubjectAltNameWarning
401 Client Error: Unauthorized

[coveralls]

Coverage decreased (-0.005%) to 38.904% when pulling 3f42f9d on mt/remove-stacktrace into 628e6c8 on master.

[codecov-io]

Codecov Report

Merging #190 into master will decrease coverage by 0.11%.
The diff coverage is 40%.

@@            Coverage Diff             @@
##           master     #190      +/-   ##
==========================================
- Coverage    82.1%   81.98%   -0.12%     
==========================================
  Files          16       16              
  Lines        1906     1910       +4     
==========================================
+ Hits         1565     1566       +1     
- Misses        341      344       +3

Impacted Files	Coverage Δ
src/crate/crash/command.py	84.48% <40%> (-0.84%)	⬇️

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[chaudum]

Print only error message instead of full stacktrack in case of connection error.

[coveralls]

Coverage decreased (-0.005%) to 38.904% when pulling c830e96 on mt/remove-stacktrace into 628e6c8 on master.