Allow full-path to certificate and remove implicit Optional::toString

Allow full-path to certificate and remove implicit Optional::toString

1) If getAAITruststoreFilename or getAAIKeystoreFilename has a file
   separator -- don't append certFilePath to filename.

2) getKeystorePath() is issuing Optional::orElse, as the code
   `+ getAAIKeystoreFilename()` is implicitly calling
   `getAAIKeystoreFilename().toString()` which yields a default toString
   e.g. "Optional[configValue]".

Issue-ID: VID-229

Change-Id: I9c135cc3dfd72cdc203b59d78162a568a6dbd688
Signed-off-by: Ittay Stern <ittay.stern@att.com>