Fix ConfigViaRestconf sometimes causing suite failure

When Robot "has bad mood", it emits an ERROR: "Error in file
'some/path/csit/libraries/ConfigViaRestconf.robot': Setting
variable 'cvr_workspace' failed: Invalid variable name
'cvr_workspace'".

The problem is that the line with the variable in the
"Settings" section is missing the "${...}" syntactic sugar
around the "cvr_workspace" variable name. This sometimes
triggers a bug in Robot that causes this malformed line to
be accepted and sometimes (very unlikely) it does not
trigger that bug, causing the abovementioned error and a
test failure caused by the fact that the variable remained
uninitialized, rendering the ConfigViaRestconf resource
inoperational.

Change-Id: Ia1c5b30234da138e4113858543971541abaa38cf
Signed-off-by: Jozef Behran <jbehran@cisco.com>