api.Filesystem in api/types.go is inconsistently used

[bufdev]

It's defined and used in some places, but in others you see stuff like:

ctx.Filesystem = "btrfs"

volume/volume.go:124:// BlockDriver needs to be implemented by block volume drivers.  Filesystem volume
volume/drivers/test/driver.go:29:   Filesystem string
volume/drivers/test/driver.go:39:       Filesystem:   string(""),
volume/drivers/test/driver.go:92:           Format:  api.Filesystem(ctx.Filesystem),
volume/drivers/aws/aws_test.go:24:  ctx.Filesystem = "ext4"
volume/drivers/btrfs/btrfs.go:80:       return api.BadVolumeID, fmt.Errorf("Filesystem format (%v) must be %v",
volume/drivers/nfs/nfs_test.go:30:  ctx.Filesystem = "nfs"
volume/drivers/btrfs/btrfs_test.go:57:  ctx.Filesystem = "btrfs"
api/types.go:85:// Filesystem supported filesystems
api/types.go:86:type Filesystem string
api/types.go:89:    FsNone Filesystem = "none"
api/types.go:90:    FsExt4 Filesystem = "ext4"
api/types.go:91:    FsXfs  Filesystem = "xfs"
api/types.go:92:    FsZfs  Filesystem = "zfs"
api/types.go:93:    FsNfs  Filesystem = "nfs"
api/types.go:100:   SpecFilesystem       = "format"
api/types.go:115:   Format Filesystem
api/types.go:156:   // Format Filesystem type if any
api/types.go:157:   Format Filesystem
api/client/client_test.go:50:   ctx.Filesystem = string("btrfs")
api/server/docker.go:139:       case types.SpecFilesystem:
api/server/docker.go:140:           spec.Format = types.Filesystem(v)
cli/volumes.go:86:      Format:           api.Filesystem(context.String("fs")),

[bufdev]

Of note, I like to use ints for enum values for this exact reason, it becomes to easy and straightforward to substitute in regular string values.

https://github.com/peter-edge/go-protolog/blob/1edbd58e6ad417bd11e64bae59ec37530ac07964/protolog.pb.go#L18

[bufdev]

This will be fixed in the refactor

[jvinod]

merged #111