Fixes #93 (Error thrown by 'hanlon config ipxe' command)

This pull request fixes #93 by removing the code that attempted to parse the iPXE script returned by a **GET** against the /config/ipxe endpoint as if it were JSON (it is not, it's an iPXE boot script).  Here's a snippet from the output before the fix in this pull request was applied:

```bash
$ hanlon config ipxe 2>&1 > t.t
$ cat t.t
[config] [generate_ipxe_script] <-710: unexpected token at '#!ipxe
...
$ 
```

and after

```bash
$ hanlon config ipxe 2>&1 > t.t
$ cat t.t
#!ipxe

:n0
isset ${net0/mac} && dhcp net0 || goto n1

echo net0 has DHCP
set dhcp_mac 01-${net0/mac:hexhyp}

:n1
isset ${net1/mac} && dhcp net1 || goto n2

echo net1 has DHCP
set dhcp_mac 01-${net1/mac:hexhyp}
...
$ 
```