libprocessgroup: fix reset of file_v2_name

ProfileAttribute::Reset does not reset file_v2_name, fix that. Also
provide ProfileAttribute::file_name() to consolidate the code.

Bug: 292636609
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
(cherry picked from commit 2ffbeaef)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:72254810d9d63f8267d32d251456a78cd4891698)
Merged-In: I5b33ca47b4fa5cabf582c8804bd13f72f6e58411
Change-Id: I5b33ca47b4fa5cabf582c8804bd13f72f6e58411