将linux-headers-$(uname -r)放在pressed.cfg中预先安装，以解决因升级Ubuntu内核后Vagra…

…nt无法识别Parallels tool的问题。

[chef/bento#551](https://github.com/chef/bento/pull/551)：
```
The issue was caused by the fact that during the box build, Linux kernel has been updated after Parallels Tools installation. Usually, it requires Parallels Tools to be re-installed. Otherwise, some kernel modules became not working.
````

http/preseed.cfg

@@ -41,6 +41,7 @@ d-i user-setup/encrypt-home boolean false
 
 #d-i pkgsel/include string openssh-server cryptsetup build-essential libssl-dev libreadline-dev zlib1g-dev linux-source dkms
 #d-i pkgsel/include string openssh-server ntp curl nfs-common linux-headers-$(uname -r) build-essential perl dkms
+d-i pkgsel/include string openssh-server linux-headers-$(uname -r) curl perl
 d-i mirror/country string manual
 d-i mirror/http/hostname string mirrors.tuna.tsinghua.edu.cn
 d-i mirror/http/directory string /ubuntu
@@ -51,7 +52,6 @@ d-i apt-setup/backports boolean true
 d-i apt-setup/services-select multiselect security
 d-i apt-setup/security_host string mirrors.tuna.tsinghua.edu.cn
 d-i apt-setup/security_path string /ubuntu
-d-i pkgsel/include string openssh-server ntp
 d-i pkgsel/install-language-support boolean false
 # Policy for applying updates.  May be "none" (no automatic updates),
 # "unattended-upgrades" (install security updates automatically), or