fetch/git: Change to use clearer ssh url syntax for broken servers

fetch/git: Change to use clearer ssh url syntax for broken servers

Some servers, e.g. bitbucket.org can't cope with ssh:// as part of
the git url syntax. git itself is happy enough with this but you
get server side errors when using it.

This changes the git fetcher to use the more common ssh url format
which also means we need a : before the path.

Seems a shame to have to do this due to broken servers however
it should be safe enough since this other form is the one most people
use on the commandline so it should be safe enough.

[YOCTO #8864]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>