libbase: return different result depend on the errno

In the RemoveFileIfExists it always return true even if error appeared
when using stat function.

It should distinguish different error. Such as ENOENT and ENOTDIR
we exactly know the file does not exist. But EACCES(current user has not
all search permission in the file path) and other errors appeared
we can't know whether file exits. So we should return false indicate
there are some error appeared.

Test: ran unit tests
Change-Id: I75788bf0621040812413d52596b5effb628fd0b1
Signed-off-by: liwugang <liwugang@xiaomi.com>