pidgin/pidgin

Clean up setting handling for the credential manager and make its unit tests don't mess up the others

Testing Done:
removed `build/libpurple/tests/config` and ran the unit tests. the `purple path` tests are still failing, but that's unrelated.

Reviewed at https://reviews.imfreedom.org/r/1826/
[wrap-file]
directory = libnice-0.1.19
source_url = https://libnice.freedesktop.org/releases/libnice-0.1.19.tar.gz
source_filename = libnice-0.1.19.tar.gz
source_hash = 6747af710998cf708a2e8ceef51cccd181373d94201dd4b8d40797a070ed47cc
[provide]
dependency_names = nice
nice=libnice_dep