[2.2.0+]dhclient lease file is not removed during deprovisioning when using NetworkManager

[yuxisun1217]

Description of problem:
In RHEL-7, the dhclient lease file under /var/lib/NetworkManager/ folder is not removed during deprovisioning.

Version-Release number of selected component (if applicable):
WALinuxAgent-2.2.0+

RHEL Version:
RHEL-7.3

How reproducible:
100%

Steps to Reproduce:

1. Prepare a RHEL-7.3 VM with WALA-2.2.0+ installed(NetworkManager enabled)
2. Run "waagent -deprovision". It shows "WARNING! Cached DHCP leases will be deleted."
3. Check dhclient lease file:
   ls /var/lib/NetworkManager/dhclient-*.lease

Actual Result:
The dhclient lease file is not removed.

Expect Result:
The dhclient lease file is removed.

Additional Info:
Currently WALA only remove all the files under /var/lib/dhclient/dhclient/. But if we use NetworkManager, the dhclient lease file is like this: /var/lib/NetworkManager/dhclient-5fb06bd0-0bb0-7ffb-45f1-d6edd65f3e03-eth0.lease