GetTLSDataFromSecret should check cert content before returning

[jamiehannaford]

GetTLSDataFromSecret retrieves the TLS secret from the API, extracts its data and returns a struct. If the user named the secret keys incorrectly, empty data is passed back and eventually they're confronted with:

tls: failed to find any PEM data in certificate input

which is slightly confusing. It would probably be better to check the content of the data before returning and raise an error there instead.

[xiang90]

@jamiehannaford agreed. can you help to improve this by sending a pr?

[raoofm]

@jamiehannaford @xiang90 I'm facing a similar issue. Can you please elaborate on

If the user named the secret keys incorrectly, empty data is passed back

I named them

[raoofm]

here #1384