Remove general assumption in get_packages()

get_packages() always included 'general' as a default 'service' file.
Remove this assumption and add it explicitly to the primary package
installation call.  This allows get_package() to be used in other places
where 'general' is not desired to be included.

Change-Id: I1eed4386d073d6ae9534aedae32654208c6662e8
diff --git a/tools/install_prereqs.sh b/tools/install_prereqs.sh
index 68f11ce..0c65fd9 100755
--- a/tools/install_prereqs.sh
+++ b/tools/install_prereqs.sh
@@ -55,7 +55,7 @@
 # ================
 
 # Install package requirements
-install_package $(get_packages $ENABLED_SERVICES)
+install_package $(get_packages general $ENABLED_SERVICES)
 
 if [[ -n "$SYSLOG" && "$SYSLOG" != "False" ]]; then
     if is_ubuntu || is_fedora; then