[BUG] walinuxagent does not read environment variable PATH

I updated the PATH variable on my VM, but the walinuxagent seems not to pick up the changes, and uses and odd value for it.
Steps followed:
- update system-wide PATH by modifying `/etc/environment`
- restart the VM

If I ssh into the machine and perform the following commands:
- `sudo su` (to impersonate the user `root`)
- `echo $PATH`
the returned value is correct.

If I execute `echo $PATH` in Azure Portal through the 'Run command' panel of the VM, a different value is returned in the output (different even from the one before I made the change).
I also executed the commands `whoami` (to be sure I am using the same user `root` in both cases) and `more /etc/environment` (to check that the right value is still there).
I tried to re-install and restart the agent, but not difference in the outcome.

- Distro and Version: Ubuntu 16.04 (Data Science Machine)
- WALinuxAgent version. Output of `waagent --version`:
WALinuxAgent-2.2.32.2 running on ubuntu 16.04
Python: 3.5.2
Goal state agent: 2.2.40

No source file or test is identified. Start by reproducing the difference between SSH as root and Azure Portal Run Command using `whoami`, `echo $PATH`, and `more /etc/environment` on Ubuntu 16.04 with WALinuxAgent 2.2.32.2. Done means the agent-run command observes the intended system-wide PATH, or the issue documents the confirmed limitation and its scope.

Written by the indexing model from the issue text.