quote the image name in image check failure errors to make it clear it is empty

[laverya]

What this PR does / why we need it:

Error: failed to validate installation: failed to create online app: failed to pull: failed to write common midstream: failed to update installation images: failed to wait for image checks: failed to check if image  is private: failed to parse docker ref "": invalid reference format

is unclear

Error: failed to validate installation: failed to create online app: failed to pull: failed to write common midstream: failed to update installation images: failed to wait for image checks: failed to check if image "" is private: failed to parse docker ref "": invalid reference format

is a little more clear

Which issue(s) this PR fixes:

Does this PR require a test?

Does this PR require a release note?

Does this PR require documentation?