Implement custom sapcontrol webservices

[fabriziosestito]

This PR decouples trento from sap_host_exporter, introducing trento/internal/sapsystems/sapcontrol containing a stripped-down version of the gowsdl generated soap webservice.
Here the sap_host_exporter original code for reference: https://github.com/SUSE/sap_host_exporter/tree/master/lib/sapcontrol

Webservice and soap client initialization has been moved away from internal/sapsystem to the webservice constructor, since we are just using a unix socket here, removing the need to use a viper configuration object.
Adds mapstructure tags to webservice result structs.

It also refactors tests by removing sap_host_exporter dependency gomock, using the mockery generator to be consistent with the rest of the project.

Resolves #79

Some questions:
should we add and link the full generated gowsdl code as reference to the documentation (see for example here: https://github.com/SUSE/sap_host_exporter/blob/master/doc/development.md#sapcontrol-web-service)?

Are the generated json/xml tags in the webservice's structs necessary?

[arbulu89]

Hi @fabriziosestito . Fantastic work!
Just added some few details.

About your questions. I think the xml annotations are needed to the marshalling, I'm not sure about the json ones. @stefanotorresi will know for sure.
If we can remove them, let's remove them.

Edit. Yes, add a link to the full autogenerated code, it will make easier for newcomers

[rtorrero]

Great work @fabriziosestito ! Thanks for the PR, I didn't find anything worth commenting other than the small typo on internal/sapsystem/sapsystem_kvstore_test.go and what was already mentioned by @arbulu89 .

[arbulu89]

@fabriziosestito Green light from my side. If you tested the changes in a real trento env, and it still works the same as before, we can merge

[fabriziosestito]

@fabriziosestito Green light from my side. If you tested the changes in a real trento env, and it still works the same as before, we can merge

I was not sure how I should confidence-test against a real trento env, so I basically exported the contents of the consul kv store from the master/this branch and compared them.

master.json
custom_sapcontrol_webservices.json

Comparing the two shows that only the key names and time-related values are changed.

Here the diff -u output for reference:
diff.output.txt

You might need to re-approve the PR since I squashed the fixup commits.

[rtorrero]

LGTM

[stefanotorresi]

great stuff!