Reorganize sapsystem data

[arbulu89]

Some improvements in the sapsystem internal code.

Disclaimer: This is the 1st change on a queue of improvements on the road for the SAP discovery mechanism. I preferred to make the PR small to make the review easier

The major change is the modification of the SAPSystem struct, which now stores multiple SAPInstances. With this, I have changed a bit the html templates to show properly multiple instances per host.

Pending things that will come later

• Get and store data in the KV storage of the DEFAULT.PFL for each SAP system. This will be needed to associate the SAP Application with the database
• Implement the method to get the SAP system identifier (some discussions in progress in internal confluence)
• Move sapsystems data in the KV storage. Now it is stored in trento/v0/hosts/$host1/sapsystems. To make it more accessible and less dependant on hosts it will be moved to trento/v0/sapsystems
• Update the SAPSystem struct to store a list of host for the instances. This will be done to make easier the visualition, and know exactly in which node is running each SAP instance (SAP instance stores the virtual hostname, which is not good for this purpose)
• And more changes in the frontend that I won't cover here now...

[arbulu89]

@stefanotorresi @rtorrero @fabriziosestito Code rebased from the main branch. Now, we should be able to review and merge

[stefanotorresi]

Way to go, Xabi!