shrinker: Fix osv_register_shrinker visibility for C apps

$ capstan run
Created instance: memory-hog
OSv v0.08
I'm a memory hog!
Failed looking up symbol osv_register_shrinker

Reported-by: Don Marti <dmarti@cloudius-systems.com>
Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
release-ec2: Choose availability zone dynamically

It turned out that set of availability zones in each region
may be different for different accounts so one should not
hard code availability zone name but choose it dynamically instead.

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
release-ec2: add parameter for OSv modules list specification

--modules-list parameter introduced

Signed-off-by: Dmitry Fleytman <dmitry@daynix.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>