Use /dev/urandom to speedup Server startup

Using /dev/urandom instead of /dev/random increases signficantly
the startup time and does not represent anymore a tangible risk
in terms of security.

Change-Id: I6c63142bbee22060df14cb6a28d38589348ca3bb

centos/7/Dockerfile

diff --git a/centos/7/Dockerfile b/centos/7/Dockerfile
index cfa7f18..cd41c08 100644
--- a/centos/7/Dockerfile
+++ b/centos/7/Dockerfile
@@ -15,6 +15,7 @@
 USER gerrit
 RUN java -jar /var/gerrit/bin/gerrit.war init --batch --install-all-plugins -d /var/gerrit
 RUN java -jar /var/gerrit/bin/gerrit.war reindex -d /var/gerrit
+RUN git config -f /var/gerrit/etc/gerrit.config container.javaOptions "-Djava.security.egd=file:/dev/./urandom"
 
 # Allow incoming traffic
 EXPOSE 29418 8080

ubuntu/16/Dockerfile

diff --git a/ubuntu/16/Dockerfile b/ubuntu/16/Dockerfile
index 87b8cd2..7edb9c0 100644
--- a/ubuntu/16/Dockerfile
+++ b/ubuntu/16/Dockerfile
@@ -18,6 +18,7 @@
 USER gerrit
 RUN java -jar /var/gerrit/bin/gerrit.war init --batch --install-all-plugins -d /var/gerrit
 RUN java -jar /var/gerrit/bin/gerrit.war reindex -d /var/gerrit
+RUN git config -f /var/gerrit/etc/gerrit.config container.javaOptions "-Djava.security.egd=file:/dev/./urandom"
 
 # Allow incoming traffic
 EXPOSE 29418 8080