Support both clientCAFile and clientCAFiles
Support both clientCAFile and clientCAFiles

Summary:
Part of deprecating clientCAFile.

Ensures that all areas that read in clientCAFile also read in clientCAFiles. We use either approach exclusively, and prioritize using clientCAFiles over clientCAFile, meaning we will first check clientCAFiles, and only if they are not present will we try to read in clientCAFile.

Currently, on config side all configs either provide client_ca_files, or both client_ca_files and client_ca_file. On client side however there are still instances of SSLContextConfigs being created that set clientCAFile directly instead of using the thrift processor. D37429044 will update them to set clientCAFiles instead, but this is a prerequisite.

After all instances of setting clientCAFile are removed, we will remove clientCAFile from the codebase entirely.

Reviewed By: xybu

Differential Revision: D37428565

fbshipit-source-id: 06b526ba73c1357fef2d355dec22d4942108c9ae

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