Do not add arcs to the soinfo graph on dlopen

While introducing RTLD_NOLOAD in b648a8a5 a change in how soinfo structs are
connected was also introduced. When calling dlopen the library that is loaded
is added as a child to the soinfo from which the caller comes - i.e. building a
dependency graph.

Unfortunately this shows issues upon unloading, such as blowing the stack if
there are loops in the graph.

This change reverts that part of b648a8a5, keeping everything as a child of the
root soinfo.

Change-Id: I604ee9210613b19f693a568158e69707620a95db
Signed-off-by: Bjorn Andersson <bjorn.andersson@sonymobile.com>