Rename apts to debs

apts aren't a thing, debs are. apt-get installs debs, like yum installs
rpms. Another option would be to rename rpms to yums, but that is even
sillier, considering then for suse we'd have to call it "zypper-suse" or
something, even though it would want to consume yums-general as a base.

Include a symlink to the old name to help out with grenade. The symlink
should go away later.

This is a long-standing annoyance of mine.

Related-to: I915f0e59c13d8cf5fb3549c6202f8aa2f8be0856
Change-Id: I0416180db5b6add996ce5b48c6966c1b68adbcb0

files/apts

@@ -0,0 +1 @@
+debs/

functions-common

@@ -945,7 +945,7 @@ function get_or_create_endpoint {
 function _get_package_dir {
     local pkg_dir
     if is_ubuntu; then
-        pkg_dir=$FILES/apts
+        pkg_dir=$FILES/debs
     elif is_fedora; then
         pkg_dir=$FILES/rpms
     elif is_suse; then
@@ -975,7 +975,7 @@ function apt_get {
 }
 
 # get_packages() collects a list of package names of any type from the
-# prerequisite files in ``files/{apts|rpms}``.  The list is intended
+# prerequisite files in ``files/{debs|rpms}``.  The list is intended
 # to be passed to a package installer such as apt or yum.
 #
 # Only packages required for the services in 1st argument will be