[ycabled] add more coverage to ycabled; add minor name change for vendor API CLI return key-values pairs (sonic-net#338)

The main motivation of this PR is improve coverage of ycabled.
While fixing unit test cases found an improvement to the name key-values returned to CLI, changed those names for keys as well

Signed-off-by: vaibhav-dahiya [email protected]

Description
Motivation and Context
How Has This Been Tested?
Unit-Tests and running the changes on testbed.

Additional Information (Optional)

Author: vdahiya12