Permit upload of symbolic link

[geaaru]

Permit upload of symbolic link with invalid link.

$ ln -s /tmp/ufo ufo
$ mottainai-cli namespace upload tmp ./ufo  /
panic: open ./ufo: no such file or directory

goroutine 1 [running]:
github.com/MottainaiCI/mottainai-cli/vendor/github.com/MottainaiCI/mottainai-server/pkg/client.(*Fetcher).UploadNamespaceFile(0xc42023bc10, 0x7fff430077f3, 0x3, 0x7fff430077f7, 0x5, 0x7fff430077fd, 0x1, 0x4, 0x4)
	/var/tmp/portage/dev-util/mottainai-cli-0.0_pre20180816/work/mottainai-cli-0.0_pre20180816/src/github.com/MottainaiCI/mottainai-cli/vendor/github.com/MottainaiCI/mottainai-server/pkg/client/artefact.go:300 +0x47a
github.com/MottainaiCI/mottainai-cli/cmd/namespace.newNamespaceUploadCommand.func1(0xc4202a9680, 0xc420287950, 0x3, 0x3)
	/var/tmp/portage/dev-util/mottainai-cli-0.0_pre20180816/work/mottainai-cli-0.0_pre20180816/src/github.com/MottainaiCI/mottainai-cli/cmd/namespace/upload.go:49 +0x234
github.com/MottainaiCI/mottainai-cli/vendor/github.com/spf13/cobra.(*Command).execute(0xc4202a9680, 0xc420287860, 0x3, 0x3, 0xc4202a9680, 0xc420287860)
	/var/tmp/portage/dev-util/mottainai-cli-0.0_pre20180816/work/mottainai-cli-0.0_pre20180816/src/github.com/MottainaiCI/mottainai-cli/vendor/github.com/spf13/cobra/command.go:766 +0x2c1
github.com/MottainaiCI/mottainai-cli/vendor/github.com/spf13/cobra.(*Command).ExecuteC(0x142f620, 0x1, 0x2, 0x1e)
	/var/tmp/portage/dev-util/mottainai-cli-0.0_pre20180816/work/mottainai-cli-0.0_pre20180816/src/github.com/MottainaiCI/mottainai-cli/vendor/github.com/spf13/cobra/command.go:852 +0x30a
github.com/MottainaiCI/mottainai-cli/vendor/github.com/spf13/cobra.(*Command).Execute(0x142f620, 0x1e, 0xbdaaa0)
	/var/tmp/portage/dev-util/mottainai-cli-0.0_pre20180816/work/mottainai-cli-0.0_pre20180816/src/github.com/MottainaiCI/mottainai-cli/vendor/github.com/spf13/cobra/command.go:800 +0x2b
github.com/MottainaiCI/mottainai-cli/cmd.Execute()
	/var/tmp/portage/dev-util/mottainai-cli-0.0_pre20180816/work/mottainai-cli-0.0_pre20180816/src/github.com/MottainaiCI/mottainai-cli/cmd/root.go:148 +0x2d
main.main()
	/var/tmp/portage/dev-util/mottainai-cli-0.0_pre20180816/work/mottainai-cli-0.0_pre20180816/src/github.com/MottainaiCI/mottainai-cli/mottainai-cli.go:53 +0x209