[BUG] Update on Ubuntu failes

**Describe the bug**
On Azure Ubuntu Linux VM; with custom-script extension; running `apt-get update && apt-get upgrade` hangs the deployment

Checking the STDOUT log we can see the package being unpacked

```log
Preparing to unpack .../walinuxagent_2.2.32-0ubuntu1~16.04.1_amd64.deb ...
```

then in the STDERR log we observe the issue

```log
debconf: unable to initialize frontend: Dialog
debconf: (Dialog frontend will not work on a dumb terminal, an emacs shell buffer, or without a controlling terminal.)
debconf: falling back to frontend: Readline
debconf: unable to initialize frontend: Readline
debconf: (This frontend requires a controlling tty.)
debconf: falling back to frontend: Teletype
dpkg-preconfigure: unable to re-open stdin:
```

Adding the string to the custom script has no effect on debconf; and thus remains blocked

```bash
#!/bin/bash
echo "Setting Frontend as Non-Interactive"
export DEBIAN_FRONTEND=noninteractive
```

Manually running the commands in a ssh session shows the failure

```log
Setting up initramfs-tools-bin (0.122ubuntu8.14) ...
dpkg: error processing package walinuxagent (--configure):
package is in a very bad inconsistent state; you should
reinstall it before attempting configuration
Processing triggers for dbus (1.10.6-1ubuntu3.3) ...
```
and
```log
Errors were encountered while processing:
walinuxagent
```

**Distro and WALinuxAgent details (please complete the following information):**
- Ubuntu 16.04
- WALinuxAgent version 2.2.32-0ubuntu1

Reproduce the failure on an Ubuntu 16.04 Azure VM using the custom-script extension and apt-get update && apt-get upgrade. Start by comparing the STDOUT and STDERR logs around walinuxagent package unpacking and configuration; done means the deployment and package upgrade complete without hanging or leaving walinuxagent inconsistent.

Written by the indexing model from the issue text.