Replace special char in openstack lb names when necessary and remove lb name validation

[alexbrand]

What this PR does

Given that we are no longer using the load balancer name as the discovered service/endpoint name, we no longer have skip load balancers that have invalid names.

However, the load balancer's name still ends up in a kubernetes label. Thus, we need to massage the load balancer name to a valid kubernetes label value.

Manual tests with openstack env

Created the following load balancers in openstack:

$ neutron --os-tenant-name heptio lbaas-loadbalancer-list
+--------------------------------------+--------------------+----------------+---------------------+----------+
| id                                   | name               | vip_address    | provisioning_status | provider |
+--------------------------------------+--------------------+----------------+---------------------+----------+
| 24664e42-a865-44a7-aa90-c94b42486ff3 | discoverytest3     | 104.145.29.182 | ACTIVE              | haproxy  |
| 2c2a6775-cbb8-40d1-b9b9-1dbb8951650d | !foo!              | 104.145.29.188 | ACTIVE              | haproxy  |
| 32801cab-480e-4363-90eb-3e90f954cd81 | hiro-lb            | 104.145.29.161 | ACTIVE              | haproxy  |
| 72b5385d-501e-4a81-81d2-5c6d16a16a92 | foo-bar_BAZ.123    | 104.145.29.187 | ACTIVE              | haproxy  |
| b8e442d4-2057-4018-8654-23b32b294084 | foo!@#$%^&*()_+bar | 104.145.29.186 | ACTIVE              | haproxy  |
| f04069fd-2821-4993-b7ec-34cce1908428 | bar:8080           | 104.145.29.185 | ACTIVE              | haproxy  |
| f21c2a81-2621-4737-aad6-ec777a9c6279 |                    | 104.145.29.149 | ACTIVE              | haproxy  |
+--------------------------------------+--------------------+----------------+---------------------+----------+

Discovered services:

$ k get svc -n heptio -o yaml | grep load-balancer
      gimbal.heptio.com/load-balancer-id: 24664e42-a865-44a7-aa90-c94b42486ff3
      gimbal.heptio.com/load-balancer-name: discoverytest3
      gimbal.heptio.com/load-balancer-id: 2c2a6775-cbb8-40d1-b9b9-1dbb8951650d
      gimbal.heptio.com/load-balancer-name: lb-foo-lb
      gimbal.heptio.com/load-balancer-id: 32801cab-480e-4363-90eb-3e90f954cd81
      gimbal.heptio.com/load-balancer-name: hiro-lb
      gimbal.heptio.com/load-balancer-id: 72b5385d-501e-4a81-81d2-5c6d16a16a92
      gimbal.heptio.com/load-balancer-name: foo-bar_BAZ.123
      gimbal.heptio.com/load-balancer-id: b8e442d4-2057-4018-8654-23b32b294084
      gimbal.heptio.com/load-balancer-name: foo----------_-bar
      gimbal.heptio.com/load-balancer-id: f04069fd-2821-4993-b7ec-34cce1908428
      gimbal.heptio.com/load-balancer-name: bar-8080
      gimbal.heptio.com/load-balancer-id: f21c2a81-2621-4737-aad6-ec777a9c6279
      gimbal.heptio.com/load-balancer-name: ""

Discovered endpoints:

k get ep -n heptio -o yaml | grep load-balancer
      gimbal.heptio.com/load-balancer-id: 24664e42-a865-44a7-aa90-c94b42486ff3
      gimbal.heptio.com/load-balancer-name: discoverytest3
      gimbal.heptio.com/load-balancer-id: 2c2a6775-cbb8-40d1-b9b9-1dbb8951650d
      gimbal.heptio.com/load-balancer-name: lb-foo-lb
      gimbal.heptio.com/load-balancer-id: 32801cab-480e-4363-90eb-3e90f954cd81
      gimbal.heptio.com/load-balancer-name: hiro-lb
      gimbal.heptio.com/load-balancer-id: 72b5385d-501e-4a81-81d2-5c6d16a16a92
      gimbal.heptio.com/load-balancer-name: foo-bar_BAZ.123
      gimbal.heptio.com/load-balancer-id: b8e442d4-2057-4018-8654-23b32b294084
      gimbal.heptio.com/load-balancer-name: foo----------_-bar
      gimbal.heptio.com/load-balancer-id: f04069fd-2821-4993-b7ec-34cce1908428
      gimbal.heptio.com/load-balancer-name: bar-8080
      gimbal.heptio.com/load-balancer-id: f21c2a81-2621-4737-aad6-ec777a9c6279
      gimbal.heptio.com/load-balancer-name: ""

Fixes #216