Avoid dpkg lock during Packer provisioner shell execution

Instead of disabling the Update Package List and Unattended Upgrade in the apt configuration,
wait until dpkg lock is released and temporarily stop the apt-daily services for the Packer duration.

```
$apt-config shell StateDir Dir::State/d
StateDir='/var/lib/apt/'
```

```
$echo $(apt-config shell StateDir Dir::State/d | sed -r "s/.*'(.*)\/?'$/\1/")/daily_lock
/var/lib/apt/daily_lock
```

Signed-off-by: Luca Carrogu <[email protected]>

Author: lukeseawalker

amis/packer_ubuntu1604.json

@@ -153,12 +153,15 @@
         "while [ ! -f /var/lib/cloud/instance/boot-finished ]; do echo 'Waiting for cloud-init...'; sleep 1; done"
       ]
     },
+    {
+      "type": "shell",
+      "inline": [
+        "sudo flock $(apt-config shell StateDir Dir::State/d | sed -r \"s/.*'(.*)\\/?'$/\\1/\")/daily_lock systemctl stop apt-daily.timer apt-daily.service"
+      ]
+    },
     {
       "type" : "shell",
       "inline" : [
-        "sudo sed -i 's/APT::Periodic::Update-Package-Lists \"1\"/APT::Periodic::Update-Package-Lists \"0\"/' /etc/apt/apt.conf.d/20auto-upgrades",
-        "sudo sed -i 's/APT::Periodic::Update-Package-Lists \"1\"/APT::Periodic::Update-Package-Lists \"0\"/' /etc/apt/apt.conf.d/10periodic",
-        "sudo sed -i 's/APT::Periodic::Unattended-Upgrade \"1\"/APT::Periodic::Unattended-Upgrade \"0\"/' /etc/apt/apt.conf.d/20auto-upgrades",
         "sudo apt-cache search build-essential",
         "sudo apt-get clean",
         "sudo apt-get update"

amis/packer_ubuntu1804.json

@@ -154,12 +154,15 @@
         "while [ ! -f /var/lib/cloud/instance/boot-finished ]; do echo 'Waiting for cloud-init...'; sleep 1; done"
       ]
     },
+    {
+      "type": "shell",
+      "inline": [
+        "sudo flock $(apt-config shell StateDir Dir::State/d | sed -r \"s/.*'(.*)\\/?'$/\\1/\")/daily_lock systemctl stop apt-daily.timer apt-daily.service"
+      ]
+    },
     {
       "type" : "shell",
       "inline" : [
-        "sudo sed -i 's/APT::Periodic::Update-Package-Lists \"1\"/APT::Periodic::Update-Package-Lists \"0\"/' /etc/apt/apt.conf.d/20auto-upgrades",
-        "sudo sed -i 's/APT::Periodic::Update-Package-Lists \"1\"/APT::Periodic::Update-Package-Lists \"0\"/' /etc/apt/apt.conf.d/10periodic",
-        "sudo sed -i 's/APT::Periodic::Unattended-Upgrade \"1\"/APT::Periodic::Unattended-Upgrade \"0\"/' /etc/apt/apt.conf.d/20auto-upgrades",
         "sudo apt-cache search build-essential",
         "sudo apt-get clean",
         "sudo apt-get update"