Checkpoint restart

We provide basic checkpoint/restart support, leveraging the original implementation from HermiTcore.

To checkpoint an application, run it with the HERMIT_CHECKPOINT environment variable set to the checkpoint frequency, in seconds. For example:

HERMIT_CHECKPOINT=2 HERMIT_TUX=1 HERMIT_ISLE=uhyve \
/tmp/hermitux/hermitux-kernel/prefix/bin/proxy \
/tmp/hermitux/hermitux-kernel/prefix/x86_64-hermit/extra/tests/hermitux program

Checkpoints will be created in a checkpoint/ folder in the local directory. To resume to the latest checkpoint, simply run the application normally from that particular folder (checkpoint/'s parent) without the environment variable set:

HERMIT_TUX=1 HERMIT_ISLE=uhyve \
/tmp/hermitux/hermitux-kernel/prefix/bin/proxy \
/tmp/hermitux/hermitux-kernel/prefix/x86_64-hermit/extra/tests/hermitux program