Fixed correct handling of OBS repositories as debian source

[csoler]

Took me a while to find this, but according to the pkg2appimage documentation, Debian repositories from the opensuse build system should be listed as:

dist: [ubuntu distrib]
sources:

• deb https://download.opensuse.org/repositories/[...]:/[software name]/[ubuntu distrib]/ /

...but in functions.sh, the parsing method employed in apt-get.update() is only compatible with the classical syntax such as

• deb http://archive.ubuntu.com/ubuntu/ [ubuntu distrib] main universe

...so it fails and doesn't fill the Packages.gz file.
The present patch solves this (probably not very elegantly).

[probonopd]

Thanks @csoler. How do you test this?

[csoler]

You just need to do this: pkg2appimage ./retroshare.yml
The file retroshare.yml is pasted below.
Also I found out that the current functions.sh doesn't actually select the latest package on OBS, probably because packages are not necessarily listed by version number, so it takes the first one in the list. If you use the patch above, you'll get a Retroshare appimage for 0.6.6. In order to force the package version, I implemented a way to specify it in the yml as
packages:
- retroshare-common=0.7.6-1
- [...]
I'll add the commit below. I totally understand if you'd prefer to to include this commit, since it adds additional syntax to yml files (yet perfectly keeps backward compatibility).

[csoler]

note that another way to go would be to fix the automated selection of latest versions of packages from OBS in functions.sh. I opted for specifying the version, as it's probably more handy. Both may be implemented of course. The retroshare.yml is attached below.
yml_file.zip

[probonopd]

Thanks @csoler