Use java version independent package on Ubuntu

Different versions of Ubuntu ship with different versions of Java.
Trusty had 7, Xenial has 8, and so on. This causes problems when we
hardcode a versioned package name into our dep lists as that version may
not exist everywhere. Thankfully Ubuntu provides a default-jre-headless
package that we can use instead that maps properly onto whatever java
version is correct.

Change-Id: I4e5da215c8f7aa426494686d5043995ce5d3c3af
diff --git a/files/debs/general b/files/debs/general
index a1f2a4b..c121770 100644
--- a/files/debs/general
+++ b/files/debs/general
@@ -2,6 +2,7 @@
 bridge-utils
 bsdmainutils
 curl
+default-jre-headless  # NOPRIME
 g++
 gcc
 gettext  # used for compiling message catalogs
@@ -17,7 +18,6 @@
 libxslt1-dev  # lxml
 libyaml-dev
 lsof # useful when debugging
-openjdk-7-jre-headless  # NOPRIME
 openssh-server
 openssl
 pkg-config