Add configurable API endpoints to server and node (#245)
Define /node/cert as alias of /node/api/cert (#245)
Fix node <-> nodeApi cardinality (1<-->0..1) (#245)
Create related default api for existing objects (#245)
Define deletion behaviour for ServerApi (#245, #487)
Merge branch 'master' into feature245
Fix Api serializers cardinality (#245)
Increase delete_orphan task verbosity.
Update database to define deletion behaviour (#487)
Update database to define deletion behaviour (#245 + #487)
Drop do-request-cert, create do-request-mgmt-cert (#234 note-19)

* Provide certificate signature as utility (do-request-mgmt-cert)
* Generate node.api.cert on firmware generation.
Fix node.api @setter: allow set /api to null (#245)
Provide Api object creation with default base_uri (#245)
Delete node.cert field (#245)
Node go DEBUG on api missconfiguration (#245 note-21)
Provide default URI when adding an API endpoint to a node (#245 note-21)
Cosmetics: mix node advanced fieldset with the main one.
Catch OperationLocked while running ping test.
Warn user on build image file missconfiguration.

Avoid uninformative 400 error when accessing to build.image.file
raises SuspiciousFileOperation becahse image.name path is outside
of image.storage.location
Handle SuspiciousFileOperation on build.state (#502)