[Libosinfo] [libosinfo 0/4] Add is-snapshot support

[Christophe Fergeau]

This patch goes on top of the 'boolean support' series, and adds support
for the 'is-snapshot' tag. Regarding patch 1/4, I set myself as the author
of the commit as it had initially more substantial changes, but now it's
very close to the initial patches from Zeeshan, so maybe the author should
be switched back (Zeeshan?). I don't care either way.

Christophe