Add skip_keyfile option for deb package

There are cases where we don't want the check for keyfile, this will add a
config option, that allows you to skip this particular check.

Fixes #1851

Signed-off-by: Jeroen van Baarsen <jeroenvanbaarsen@gmail.com>

debian/preinst

@@ -27,7 +27,8 @@ case "$1" in
       exit 0
     fi
 
-    if [ -z "${DEBCONF_RECONFIGURE}" ]; then
+    db_get "dokku/skip_key_file"
+    if [ -z "${DEBCONF_RECONFIGURE}" ] && [ "$RET" != "true" ]; then
       db_get "dokku/key_file"
       if [ ! -f "$RET" ]; then
           echo "Error: keyfile '$RET' not found."

debian/templates

@@ -13,6 +13,11 @@ Description: Hostname or IP for server:
 Type: string
 Default: dokku.me
 
+Template: dokku/skip_key_file
+Description: Skip key file requirement?
+Type: boolean
+Default: false
+
 Template: dokku/key_file
 Description: Keyfile for initial user:
 Type: string