allow setting up an apt package cache for the build server setup

This creates a cache folder which will store the apt cache from the VM.

examples/makebuildserver.config.py

@@ -21,6 +21,13 @@
 #
 # cachedir = 'buildserver/cache'
 
+# A big part of creating a new instance is downloading packages from Debian.
+# This setups up a folder in ~/.cache/fdroidserver to cache the downloaded
+# packages when rebuilding the build server from scratch.  This requires
+# that virtualbox-guest-utils is installed.
+#
+# apt_package_cache = True
+
 # To specify which Debian mirror the build server VM should use, by
 # default it uses http.debian.net, which auto-detects which is the
 # best mirror to use.

makebuildserver

@@ -54,6 +54,7 @@ config = {
         'https://f-droid.org/jessie32.box',
     ],
     'debian_mirror': 'http://http.debian.net/debian/',
+    'apt_package_cache': False,
     'boot_timeout': 600,
     'cachedir': cachedir,
     'cpus': 1,
@@ -374,6 +375,14 @@ if cachedir != 'buildserver/cache':
   config.vm.synced_folder '{0}', '/vagrant/cache'
 """.format(cachedir)
 
+# cache .deb packages on the host via a mount trick
+if config['apt_package_cache']:
+    aptcachedir = cachedir + '/apt/archives'
+    vagrantfile += """
+  config.vm.synced_folder "{0}", "/var/cache/apt/archives",
+    owner: 'root', group: 'root', create: true
+""".format(aptcachedir)
+
 vagrantfile += """
   config.vm.provision :chef_solo do |chef|
     chef.cookbooks_path = "cookbooks"