devstack ovs: get correct kernel rpm version on customed kernel
devstack ovs: get correct kernel rpm version on customed kernel

When building custom kernel version
uname -r returns 4.10.0-00054-ge4cd924
but the rpm name is kernel-4.10.0_00054_ge4cd924-1.x86_64
This is because dash is illegal character in rpm version

This patch fix the kernel version is rpm based OS
but converting all the dashes to underscores

Change-Id: I3d0981fbe30f2436f00c200919b50aeb97491252

eayunstack/neutron,noironetworks/neutron,eayunstack/neutron,openstack/neutron,huntxu/neutron,openstack/neutron,mahak/neutron,openstack/neutron,mahak/neutron,noironetworks/neutron,mahak/neutron,huntxu/neutron