[BUG] wala agent tried to install LIS driver in CentOS 7.8

**Describe the bug: A clear and concise description of what the bug is.**
LIS installation is only available less than RHEL/CentOS 7.7. There is no need it in 7.8 or higher version.

Note: Please add some context which would help us understand the problem better
1. Provision CentOS 7.8
2. Serial console output
3. Steps to reproduce the behavior.

**Distro and WALinuxAgent details (please complete the following information):**
- Distro and Version: [e.g. Ubuntu 16.04]
- WALinuxAgent version [e.g. 2.2.40, you can copy the output of `waagent --version`, more info [here](https://github.com/Azure/WALinuxAgent/wiki/FAQ#what-does-goal-state-agent-mean-in-waagent---version-output) ]

**Additional context**
This is the waagent log.

2020/08/18 18:08:23.039358 INFO Daemon Run daemon
2020/08/18 18:08:23.048474 INFO Daemon cloud-init is enabled: True
2020/08/18 18:08:23.051340 INFO Daemon Using cloud-init for provisioning
2020/08/18 18:08:23.054655 INFO Daemon Clean protocol
2020/08/18 18:08:23.058514 INFO Daemon Provisioning already completed, skipping.
2020/08/18 18:08:33.097048 INFO Daemon RDMA: kvp daemon (hypervkvpd) is running
2020/08/18 18:08:33.098664 INFO Daemon RDMA: kvp daemon running: True
2020/08/18 18:08:43.110361 INFO Daemon RDMA: found firmware version: 144.0
2020/08/18 18:08:43.143359 INFO Daemon RDMA: driver package is NOT installed
2020/08/18 18:08:43.144394 INFO Daemon RDMA: updating RDMA packages
2020/08/18 18:08:43.145273 INFO Daemon RDMA: refreshing yum repos
2020/08/18 18:08:45.316039 INFO Daemon RDMA: repositories refreshed
2020/08/18 18:08:45.317615 INFO Daemon RDMA: Force installing package: msft-rdma-drivers
2020/08/18 18:08:50.347330 INFO Daemon RDMA: installation completed: msft-rdma-drivers
2020/08/18 18:08:50.348594 INFO Daemon RDMA: **pkgs dir: /opt/microsoft/rdma/rhel78**
2020/08/18 18:08:50.352623 ERROR Daemon Event: name=WALinuxAgent, op=UnhandledError, message=Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/azurelinuxagent/daemon/main.py", line 81, in run
self.daemon(child_args)
File "/usr/lib/python2.7/site-packages/azurelinuxagent/daemon/main.py", line 144, in daemon
self.rdma_handler.install_driver_if_needed()
File "/usr/lib/python2.7/site-packages/azurelinuxagent/common/rdma.py", line 157, in install_driver_if_needed
self.install_driver()
File "/usr/lib/python2.7/site-packages/azurelinuxagent/pa/rdma/centos.py", line 79, in install_driver
self.update_rdma_package(fw_version)
File "/usr/lib/python2.7/site-packages/azurelinuxagent/pa/rdma/centos.py", line 109, in update_rdma_package
self.install_rdma_drivers(fw_version)
File "/usr/lib/python2.7/site-packages/azurelinuxagent/pa/rdma/centos.py", line 148, in install_rdma_drivers
raise Exception('RDMA packages directory %s is missing' % pkg_dir)
Exception: RDMA packages directory /opt/microsoft/rdma/rhel78 is missing
, duration=0
2020/08/18 18:08:50.354927 WARNING Daemon Daemon ended with exception -- Sleep 15 seconds and restart daemon

There is no rhel78 directory

[root@controller-vm infiniband]# cd /opt/microsoft/rdma/rhel
rhel610/ rhel65/ rhel68/ rhel69/ rhel71/ rhel72/ rhel73/ rhel74/ rhel75/
[root@controller-vm infiniband]#

**Log file attached**
If possible, please provide the full /var/log/waagent.log file to help us understand the problem better and get the context of the issue.

I have a full log. Please reach out to me.