Fix ceilometer.conf.sample mismatch

ceilometer.conf.sample mismatch issue makes the tests failing. This patch
removes the checkupdate.sh test from tox.ini, like it was removed from nova
too, until having a proper solution for handling the changes in
ceilometer.conf.sample, to fix the gate quickly.

Closes-Bug: #1297999

Change-Id: I7889580b3df2d30d80703d7ef540194e7f71ec51