Apply a variation of the suggested app-level patch to SecureRandom

http://android-developers.blogspot.pt/2013/08/some-securerandom-thoughts.html
for more details. This isn't an ideal solution, but until a proper patch
comes up it'll do

Change-Id: Ib6bf4478fc1ae3d16eefa4eb2ad90f1f3e9de021
Do not apply the PRNG workarounds if an explicit seed is given

If the caller seeds the engine, do NOT override that seed with another
from urandom.

This is a companion change to Ib6bf4478fc1ae3d16eefa4eb2ad90f1f3e9de021,
and should be reverted along with it when the proper fix appears.

Change-Id: I0a9ba35d74af89c91b6aafa35cc94001372794e1