[201811][sonic-config-engine] Parse AutoNegotiation element from LinkMetadata section of minigraph file

[jleveque]

Backport of #7031 to the 201811 branch

Why I did it

To enable parsing the AutoNegotiation element from the LinkMetadata section of minigraph file

How I did it

Parse the value AutoNegotiation element from the LinkMetadata section of minigraph file. If the element is present, an autoneg key will be added to the port in the PORT table of Config DB with a value of either 0 or 1

If an autoneg value is present in port_config.ini, the value from the minigraph will take precedence, overriding that value.

Also remove AutoNegotiation and EnableAutoNegotiation elements from the DeviceInfo section, as we will use this data in the LinkMetadata section to determine whether to enable auto-negotiation for a port.

How to verify it

Added unit tests to validate the behavior described above

[lguohan]

can you check the build failure?

[jleveque]

All checks have now passed except LGTM, which is having trouble locating a commit :/

I believe this PR is good to merge.