Link OCAFExport_test against FWOSPlugin and TKBin

This is the same problem as in commit e9ad629, this test
loads FWOSPlugin and TKBin at run-time.  Since there is
currently no way to tell plugin directory at runtime, it is
simpler to directly link against these libraries.

Moreover set CSF_PluginDefaults and CSF_PluginUserDefaults environment
variable when running this test to load resource file from the build
tree.
Merge pull request #381 from tpaviot/review/fix-OCAFExport_test

Link OCAFExport_test against FWOSPlugin and TKBin