Undefined names: Missing imports

[cclauss]

DIscovered by #141 and related to #305... flake8 testing of https://github.com/mingrammer/diagrams

% flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics

./diagrams/oci/database.py:85:7: F821 undefined name 'AutonomousDatabase'
ADB = AutonomousDatabase
      ^
./diagrams/oci/database.py:86:12: F821 undefined name 'AutonomousDatabaseWhite'
ADBWhite = AutonomousDatabaseWhite
           ^
./diagrams/oci/database.py:87:13: F821 undefined name 'Databaseservice'
DBService = Databaseservice
            ^
./diagrams/oci/database.py:88:18: F821 undefined name 'DatabaseserviceWhite'
DBServiceWhite = DatabaseserviceWhite
                 ^
4     F821 undefined name 'AutonomousDatabase'
4

https://flake8.pycqa.org/en/latest/user/error-codes.html

On the flake8 test selection, this PR does not focus on "style violations" (the majority of flake8 error codes that psf/black can autocorrect). Instead, these tests are focus on runtime safety and correctness:

• E9 tests are about Python syntax errors usually raised because flake8 can not build an Abstract Syntax Tree (AST). Often these issues are a sign of unused code or code that has not been ported to Python 3. These would be compile-time errors in a compiled language but in a dynamic language like Python, they result in the script halting/crashing on the user.
• F63 tests are usually about the confusion between identity and equality in Python. Use ==/!= to compare str, bytes, and int literals is the classic case. These are areas where a == b is True but a is b is False (or vice versa). Python >= 3.8 will raise SyntaxWarnings on these instances.
• F7 tests logic errors and syntax errors in type hints
• F82 tests are almost always undefined names which are usually a sign of a typo, missing imports, or code that has not been ported to Python 3. These also would be compile-time errors in a compiled language but in Python, a NameError is raised which will halt/crash the script on the user.

[mingrammer]

I'll check it. Thank you for reporting it.

[Wildcarde]

a few seem to have been removed since last time I used the oci entries:

• diagrams.oci.edge
• 'Filestorage' from 'diagrams.oci.storage'

I don't strictly need either of these, i was just using the 'emaildelivery' from oci.edge as a generic email (would be nice to just have postfix or even just 'email' in the onprem section if possible?). And the 'filestorage' to just indicate on prem nfs (would similarly be super helpful to have onprem.storage for the nfs)