[kvm/docs] Improve KVM setup instructions

[daall]

Signed-off-by: Danny Allen daall@microsoft.com

Description of PR

Summary: Improve KVM setup instructions
Fixes # (issue)

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• Test case(new/improvement)

Approach

What is the motivation for this PR?

I received some feedback while helping people onboard to the KVM testbed:

1. Not all VMs have ethtool installed by default, which can cause some strange errors.
2. There was some confusion over how to access sonic-mgmt inside the docker container.
3. Certain VM configurations (namely Hyper-V) require nested virtualization to be enabled explicitly in order to run KVM VMs inside them.
4. It's not clear how to check if the tests/testbed is working after all of these setup steps are complete.

How did you do it?

1. Added ethtool to the setup script.
2. Added clarification for the mount point for sonic-mgmt.
3. Added an explicit mention of nested virt.
4. Added a step to run the bgp_fact test.

How did you verify/test it?

Verified that the setup scripts work as described, and are idempotent.

Any platform specific information?

Supported testbed topology if it's a new test case?

Documentation

[lguohan]

retest this please

[prsunny]

If it returns the output as below, then this step fails. May be we should just add br1 even if it exists..

STEP 5: Checking if bridge br1 already exists...
bridge name	bridge id		STP enabled	interfaces
br1		can't get info No such device