adding FloatOpt to the config parser

This patch just adds the ability to parse Float values from a config
using oslo.config.cfg FloatOpt class

Signed-off-by: AJ Ragusa <aragusa@grnoc.iu.edu>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
ofctl_v1_2/3: fix POP_MPLS action and some match fields

The following action and match field causes an error at mod_flow_entry command.

  - ofctl_v1_2.py
    * action: POP_MPLS
    * match field: metadata, mpls_label, ipv6_nd_target

  - ofctl_v1_3.py
    * action: POP_MPLS
    * match field: in_phy_port, ipv6_nd_target

this patch fixes them.

Signed-off-by: TAKAHASHI Minoru <takahashi.minoru7@gmail.com>
unit test for ofctl_v1_2/3

Signed-off-by: TAKAHASHI Minoru <takahashi.minoru7@gmail.com>
test_ofctl:fixes pep8

Signed-off-by: TAKAHASHI Minoru <takahashi.minoru7@gmail.com>