Replace Entropy with RAND_bytes

/dev/urandom is not an approved random number generator
for NIAP certification. Changing to use BoringSSL's
RAND_bytes(), which is approved.

Bug: 121272336
Test: Ran Keystore CTS tests against Walleye
Change-Id: I579d140ef56c90b477b0d8989e3b02375681aee8
10 files changed