Fix the undefined method 'chomp' for nil:NilClass error seen with ovs 2.10
Fix the undefined method 'chomp' for nil:NilClass error seen with ovs 2.10

puppet-ovn uses puppet-vswitch to configure the OVN params. When OVS binaries are
compiled with dpdk support and when vs_config provider runs the command
'ovs-vsctl list Open_vSwitch .', the below warning messages are seen and
are part of the command output.

----
PMD: net_mlx5: cannot load glue library: libibverbs.so.1: cannot open shared
object file: No such file or directory
PMD: net_mlx5: cannot initialize PMD due to missing run-time dependency on
rdma-core libraries (libibverbs, libmlx5)
----

We see the error 'undefined method 'chomp' for nil:NilClass' when the result is
extracted. This patch fixes this issue by checking if the 'value' var is nil or
not before 'parse_column_value' is called.

Tripleo deployment with OVN is failing because of this issue.

Change-Id: I415a6229a0fbc1b55451e3738539735afdc6f8f4
Closes-bug: #1789236

openstack/puppet-vswitch,openstack/puppet-vswitch