Default config picks up OVS variants

Default config picks up OVS variants

Running a test with vanilla-ovs, vhost-user-ovs,
vhost-cuse-ovs,... does not require any building
or configuration changes - the vswitch needs only
to specified on the command line.
The config file contains new variables for particular
ovs build.
OvsVanilla:
OVS_DIR_VANILLA, QEMU_DIR_VANILLA
VhostCuse:
RTE_SDK_CUSE, OVS_DIR_CUSE, QEMU_DIR_CUSE
VhostUser:
RTE_SDK_USER, OVS_DIR_USER, QEMU_DIR_USER
The vspef chooses right paths according to command line
switches '--vswitch' (or 'VSWITCH') and '--vnf' (or 'VNF')

JIRA: VSPERF-86

Change-Id: I22e3a7f9e21d6ceb13830e444716b4274314560c
Signed-off-by: Radek Zetik <radekx.zetik@intel.com>
Reviewed-by: Maryam Tahhan <maryam.tahhan@intel.com>
Reviewed-by: Brian Castelli <brian.castelli@spirent.com>
Reviewed-by: Gene Snider <eugene.snider@huawei.com>
Reviewed-by: Al Morton <acmorton@att.com>
Reviewed-by: Tv Rao <tv.rao@freescale.com>