Exit the resolver if publishing fails

[ceason]

Currently, when there is a problem publishing an image a message will be printed to stderr, but the resolver still tries to resolve the template anyway. The output looks successful (valid yaml on stdout and a returncode of 0) but has one or more problems:

• Image is output unmodified (tag not resolved to a digest)
• Image is resolved to the currently published digest (ie not the digest of the container_image dependency)

It turns out logging.fatal() is actually an alias for logging.critical() (which does not exit the process when invoked), thus the need for explicitly exiting.

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[chrislovecnm]

/ok-to-test

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[chrislovecnm]

@nlopezgi @erain can we get a ok-to-test on this? Also it is ready to merge?

[erain]

/ok-to-test

[erain]

Sorry for the delay! I triggered another round of test and I will merge it once the test finished.