vdsm: fix typo: vcpuLimit - 'limit' was in lower-case

There are several occurences with 'Limit' so it seems that is just typo
(only one occurence with lower case).

Change-Id: I3cee77cdc6832cc6fd8be19a53087c727e028245
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1143992
Signed-off-by: Martin Pavlasek <mpavlase@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34213
Reviewed-by: Martin Sivák <msivak@redhat.com>
Tested-by: Martin Sivák <msivak@redhat.com>
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>