Bug 4267: Fix Tcpmd5user suite

Bug 4267: Fix Tcpmd5user suite

Bug 3753 was causing failures that can be avoided by
making changes described at Bug 4267.
The tcpmd5user suite was changes to both detect Bug 3753 symptom
and apply the workaround so that testing can proceed.

This required changes to ConfigViaRestconf library:
+ Added GET methods, useful for checking the configuration change was applied.
+ Added support for JSON data.
+ Including normalization provided by HsfJson library.
+ Deviations are now Logged as diff.
+ Configurable workspace to store files being diffed.
+ All this in Verify_* keywords.
+ Added "Readme" text to library documentation.

Change-Id: I52edd0503620f2459ff829dc786bfe208d9242b7
Signed-off-by: Vratko Polak <vrpolak@cisco.com>