Allow Launchpad Git URLs

This is relevant in the parser: paste.ubuntu.com/18529081/

@Daniel git:// URLs should already be autodetected. For git+ssh:// URLs, I would like to see a use case of an anonymous clone of a source (which is what Snapcraft does) with that URL prefix, because imho it's not common enough (if even present) to autodetect.

As for https://git.launchpad.net/~snappy-hwe-team/snappy-hwe-snaps/+git/tpm , we could have a solution of autodetecting http(s)://git* URLs. Another possibility would be to autodetect http(s)://git.launchpad.net* URLs, which I don't like because that would mean we have to add every exception out there to Snapcraft, which isn't feasable. So I would prefer the http(s)://git* solution.

Thoughts from anyone?

I don't have much of an opinion on this one. It'd just be nice if all possible URLs advertised on LP (https://git.launchpad.net/~snappy-hwe-team/snappy-hwe-snaps/+git/tpm) work automatically.

I noticed this is tagged with 'bitesize'. I'd like to attempt to resolve this one however I need a bit more info on how I can reproduce this.

I have cloned https://github.com/snapcore/snapcraft but I can't see the:

/bin/snapcraft-parser file listed in Daniels' pastebin entry.

Where does this come from ?

```daniel@daydream:/tmp/test$ ~/dev/snappy/snapcraft/bin/snapcraft-parser -d -i https://wiki.ubuntu.com/snapcraft/parts?action=raw
Processing part 'qt5conf'
Klone nach '/tmp/qt5conf' ...
1remote: Counting objects: 5, done.
remote: Compressing objects: 100% (5/5), done.
remote: Total 5 (delta 0), reused 4 (delta 0), pack-reused 0
Entpacke Objekte: 100% (5/5), Fertig.
Prüfe Konnektivität ... Fertig.
Processing part 'qt4conf'
Klone nach '/tmp/qt4conf' ...
remote: Counting objects: 5, done.
remote: Compressing objects: 100% (5/5), done.
remote: Total 5 (delta 0), reused 2 (delta 0), pack-reused 0
Entpacke Objekte: 100% (5/5), Fertig.
Prüfe Konnektivität ... Fertig.
Processing part 'gtkconf'
Klone nach '/tmp/gtkconf' ...
remote: Counting objects: 5, done.
remote: Compressing objects: 100% (5/5), done.
^Tremote: Total 5 (delta 0), reused 4 (delta 0), pack-reused 0
Entpacke Objekte: 100% (5/5), Fertig.
Prüfe Konnektivität ... Fertig.
Processing part 'curl'
Klone nach '/tmp/curl' ...
remote: Counting objects: 4, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 4 (delta 0), reused 3 (delta 0), pack-reused 0
Entpacke Objekte: 100% (4/4), Fertig.
Prüfe Konnektivität ... Fertig.
Processing part 'mqtt-paho'
Klone nach '/tmp/mqtt-paho' ...
remote: Counting objects: 3, done.
remote: Compressing objects: 100% (2/2), done.
remote: Total 3 (delta 0), reused 3 (delta 0), pack-reused 0
Entpacke Objekte: 100% (3/3), Fertig.
Prüfe Konnektivität ... Fertig.
Processing part 'ffmpeg'
Klone nach '/tmp/ffmpeg' ...
remote: Counting objects: 4, done.
remote: Compressing objects: 100% (4/4), done.
remote: Total 4 (delta 0), reused 0 (delta 0), pack-reused 0
Entpacke Objekte: 100% (4/4), Fertig.
Prüfe Konnektivität ... Fertig.
Processing part 'desktop'
Klone nach '/tmp/desktop' ...
remote: Counting objects: 36, done.
remote: Compressing objects: 100% (30/30), done.
remote: Total 36 (delta 5), reused 24 (delta 2), pack-reused 0
Entpacke Objekte: 100% (36/36), Fertig.
Prüfe Konnektivität ... Fertig.
Processing part 'tpm-tools'
Traceback (most recent call last):
  File "/home/daniel/dev/snappy/snapcraft/bin/snapcraft-parser", line 29, in <module>
    snapcraft.internal.parser.main()
  File "/home/daniel/dev/snappy/snapcraft/snapcraft/internal/parser.py", line 77, in main
    return run(args)
  File "/home/daniel/dev/snappy/snapcraft/snapcraft/internal/parser.py", line 248, in run
    master_parts_list = _process_index(output)
  File "/home/daniel/dev/snappy/snapcraft/snapcraft/internal/parser.py", line 222, in _process_index
    parts_list, after_parts = _process_entry(data)
  File "/home/daniel/dev/snappy/snapcraft/snapcraft/internal/parser.py", line 182, in _process_entry
    sources.get(origin_dir, None, options)
  File "/home/daniel/dev/snappy/snapcraft/snapcraft/internal/sources.py", line 352, in get
    handler_class = _get_source_handler(source...

we have source-type for this