AMBARI-4265. Provide way to set http proxy for Ambari Server (Jeff Sposetti via ncole)

ambari-server/conf/unix/ambari-env.sh

@@ -15,4 +15,4 @@
 
 
 AMBARI_PASSHPHRASE="DEV"
-export AMBARI_JVM_ARGS='-Xms512m -Xmx2048m -Djava.security.auth.login.config=/etc/ambari-server/conf/krb5JAASLogin.conf -Djava.security.krb5.conf=/etc/krb5.conf -Djavax.security.auth.useSubjectCredsOnly=false'
+export AMBARI_JVM_ARGS=$AMBARI_JVM_ARGS' -Xms512m -Xmx2048m -Djava.security.auth.login.config=/etc/ambari-server/conf/krb5JAASLogin.conf -Djava.security.krb5.conf=/etc/krb5.conf -Djavax.security.auth.useSubjectCredsOnly=false'