Fix bashism in NovaEvacuate

Tox syntax-check is failing because of a bashism in NovaEvacuate.

$ tox -e syntax-check
syntax-check installed:
syntax-check runtests: PYTHONHASHSEED='1152052790'
syntax-check runtests: commands[0] | bash -c /home/eillnor/work/openstack-resource-agents/utils/syntax_check.sh -a -p
possible bashism in /tmp/tmp.cRSar6D0il line 259 (<() process substituion):
        attrd_updater -n evacuate -A \
            2> >(grep -v "attribute does not exist" 1>&2) |
Syntax Test FAILED: syntax errors found in the following files:

/home/eillnor/work/openstack-resource-agents/ocf/NovaEvacuate
ERROR: InvocationError: '/bin/bash -c /home/eillnor/work/openstack-resource-agents/utils/syntax_check.sh -a -p'
__________________________________ summary __________________________________

ERROR: syntax-check: commands failed