Teach replace_platform_plugins_with_symlinks.sh to symlink dropins deps
This way we can have symlinking done in one place here rather than
also requiring we do some in the spec file

Change-Id: If9a39e939436d8eebf9b104134335d51bf5bed34
Signed-off-by: Mat Booth <mat.booth@redhat.com>
Reviewed-on: https://git.eclipse.org/r/30022
Reviewed-by: Alexander Kurtakov <akurtako@redhat.com>
Tested-by: Alexander Kurtakov <akurtako@redhat.com>