[fedora-build-service] #17: Replace return code based error handling by custom exception class

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#17: Replace return code based error handling by custom exception class
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 Reporter:  amitksaha       |      Owner:  somebody
     Type:  defect          |     Status:  new
 Priority:  major           |  Milestone:
Component:  Image Building  |    Version:
 Keywords:                  |
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 The code uses return codes to detect and handle/report errors. This is not
 very easy to implement and track errors. Perhaps a custom exception
 class(es) can be used in place.

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Ticket URL: <https://fedorahosted.org/fedora-build-service/ticket/17>
fedora-build-service <https://fedorahosted.org/fedora-build-service>
A service to build fedora images with a somewhat arbitrary package set from the standard
fedora repos or builds from koji.