update to firecracker-go-sdk v0.15.0

[samuelkarp]

Issue #, if available:
Fixes #121

Description of changes:
Updating the SDK is sufficient to work with Firecracker v0.15.0, though the quickstart guide no longer works and the getting started guide also needs to be updated; Firecracker's built-in seccomp enforcement is unhappy with glibc and needs to be built with musl libc.

I can either do the guide updates as part of this same PR or as a separate one; let me know which is preferred.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[samuelkarp]

Demo

[ec2-user@ip-172-31-38-164 ~]$ firecracker --version
firecracker 0.15.0
[ec2-user@ip-172-31-38-164 ~]$ uname -a
Linux ip-172-31-38-164.us-west-2.compute.internal 4.14.97-90.72.amzn2.x86_64 #1 SMP Tue Feb 5 20:46:19 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
[ec2-user@ip-172-31-38-164 ~]$ sudo /usr/local/bin/ctr run \
      --snapshotter firecracker-naive \
      --runtime aws.firecracker \
      --tty \
      docker.io/library/debian:latest\
      test
root@localhost:/# uname -a
Linux localhost 4.14.55-84.37.amzn2.x86_64 #1 SMP Wed Jul 25 18:47:15 UTC 2018 x86_64 GNU/Linux
root@localhost:/# cat /etc/os-release
PRETTY_NAME="Debian GNU/Linux 9 (stretch)"
NAME="Debian GNU/Linux"
VERSION_ID="9"
VERSION="9 (stretch)"
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

[xibz]

[nmeyerhans]

🎉

[samuelkarp]

Opened #127 for the quickstart guide. I'll merge this now and follow up with that separately.