crash-tests: prevent the process from getting stuck when there's not enough entropy

The update of the `rand` crate changed the entropy requirements for the
test binary used by the crash-tests, and now the binary gets stuck
indefinetely waiting for entropy to generate the random file name. Fixed
by simply making `/dev/random` a symlink to `/dev/urandom` in the test
virtual machine.

Author: andreacorbellini

crash-tests/linux/init.sh

@@ -17,6 +17,8 @@ if grep -q test.verify /proc/cmdline; then
   poweroff -f
 fi
 
+ln -sf /dev/urandom /dev/random
+
 echo 'Running test binary'
 atomic-write-file-test