FetchCommand: Fix detection of submodule recursion mode

FetchCommand: Fix detection of submodule recursion mode

The submodule.name.fetchRecurseSubmodules value was being read from the
configuration of the submodule, but it should be read from the config
of the parent repository.

Also, the fetch.recurseSubmodules value from the parent repository's
configuration was not being considered at all.

Fix both of these and add tests. Now the precedence of the recurse mode
is determined as follows:

 1. Value passed to the API
 2. Value configured in submodule.name.fetchRecurseSubmodules
 3. Value configured in fetch.recurseSubmodules
 4. Default to "on demand"

Change-Id: Ic23b7c40b5f39135fb3fd754c597dd4bcc94240c