Be more informative on command failures

[yakky]

We were not returning the error message when something goes wrong in migrate command

[coveralls]

Coverage decreased (-0.7%) to 94.32% when pulling f9697ff on hotfix/more_verbose into cdacfd8 on release/0.9.x.

[codecov]

Codecov Report

Merging #319 into release/0.9.x will decrease coverage by 0.01%.
The diff coverage is 100%.

@@                Coverage Diff                @@
##           release/0.9.x     #319      +/-   ##
=================================================
- Coverage          89.83%   89.81%   -0.02%     
=================================================
  Files                  7        7              
  Lines                659      658       -1     
  Branches             141      141              
=================================================
- Hits                 592      591       -1     
  Misses                33       33              
  Partials              34       34

Impacted Files	Coverage Δ
djangocms_installer/django/__init__.py	90.63% <100%> (-0.04%)	⬇️

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[coveralls]

Coverage decreased (-2.4%) to 92.587% when pulling ebd032e on hotfix/more_verbose into cdacfd8 on release/0.9.x.

[coveralls]

Coverage decreased (-0.008%) to 95.008% when pulling ebd032e on hotfix/more_verbose into cdacfd8 on release/0.9.x.