Use python abc in DeletableResource class

Fix pylint error about NotImplemented raised instead of
NotImplementedError.

Use the abc class instead of NotImplementedError.

Partial-Bug: #1346797

Change-Id: I50df1edf5c6b5c7a5c385a6389da97ffffea4d07
Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge "Use python abc in DeletableResource class"