Additionally remove support for arm6vl in release, since
go 1.8 the support for armv6 has been dropped and we do
not see high usage events from this platform.
Currently due to the occurrence of 6 arguments from
`gen-ldflags.go` leads to a bug where the binaries
genenerated have wrong names.
As shown below.
```
If you want to build for all, Just press Enter: linux/amd64
--> linux/amd64:github.com/minio/minio
$ ls release/linux-amd64/
[2017-05-04 23:08:51 PDT] 17MiB minio
[2017-05-04 23:08:51 PDT] 17MiB minio.2017-05-05T06:08:22Z
[2017-05-04 23:08:51 PDT] 76B minio.shasum
```
This PR fixes this issue by retaining the previous release
binary names.
```
If you want to build for all, Just press Enter: linux/amd64
--> linux/amd64:github.com/minio/minio
$ ls release/linux-amd64/
[2017-05-04 23:08:51 PDT] 17MiB minio
[2017-05-04 23:08:51 PDT] 17MiB minio.RELEASE.2017-05-05T06-08-22Z
[2017-05-04 23:08:51 PDT] 76B minio.shasum
```
