webadmin,root: Control scope of cookies in root webapp

This patch ensures that both "langPageShown" and "locale"
cookies are explicitly scoped to root webapp context URL,
i.e. cookie path is "/".

The reason for scoping both cookies to "/" path is to make
them visible (available) to server-side code regardless of
the current request (i.e. /docs/xxx).

Change-Id: Id3beef969b96bad40bbeef86708c7f62b3b690ad
Bug-Url: https://bugzilla.redhat.com/966525
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>