fix openvswitch requirement check

With VXLAN enabled on openvswitch, neutron checks
module version of the openvswitch kernel module.
If the pattern to extract the version matches twice
(eg. for path and version) the agent dies.

This patch ensures, that only the version is checked
against the pattern.

Change-Id: I879624f6b0936cab59e02958ae3a89950df773bb
Closes-Bug: #1322139
Merge "fix openvswitch requirement check"