[trac] avoid overwriting dropdown defaults when provisioning

[philll]

Environment

Trac instance installed for ABP

How to reproduce

1. Provision the trac instance with vagrant
2. Log in to the trac instance at ​https://issues.adblockplus.org
3. Click "New Issue"

Observed behaviour

The preset values of the fields "Priority" and "Component" are "P1" and "ABP-Android" respectively.

Expected behaviour

As set previously via Trac frontend admin, the default values should be "Unknown" for both fields.

[trev]

This shouldn't be set in the frontend but rather in the trac.ini we deploy:

[ticket]
default_component = Unknown
default_priority = Unknown
default_resolution = fixed
default_type = defect

[philll]

Setting those defaults in the config file means we have to change it every time we rename the vaue. As the frontend admin offers this possibility as well as setting the default database-wise, I would recommend not using the config file to avoid confusion.

[trev]

The frontend doesn't set this in the database but rather in trac.ini - the very settings I listed.

[philll]

​https://hg.adblockplus.org/infrastructure/rev/35c512f26fac