Makefile: update targets to better track build artifacts

[marcov]

Update Makefile so that build artifacts are actually tracked as make targets. This is to enforce a strict prerequisite ordering and better handle parallel builds.

Fixes: #157

[marcov]

Realized I need to update README.md too.

[jodh-intel]

Thanks @marcov!

lgtm

[marcov]

@jodh-intel tests are failing, looks like this is the reason but cant say for sure:

Error downloading packages:
  procps-ng-3.3.10-17.2.h5.x86_64: [Errno 256] No more mirrors to try.
  krb5-libs-1.14.1-26.h2.x86_64: [Errno 256] No more mirrors to try.

The command '/bin/sh -c yum -y update && yum install -y yum git make gcc coreutils' returned a non-zero code: 1
INFO: ERROR: test failed

[jodh-intel]

@marcov - yep, looks like a euleros issue (probably network). I've restarted it on 16.04 to see if it's transitory.

[jcvenegas]

@marcov @jodh-intel eulerOS failed again, restarting one more time...

[jcvenegas]

lgtm

[jcvenegas]

@kata-containers/documentation ping

[jodh-intel]

Restarting failing CI's again...

[marcov]

tests are happy now 😄

[jodh-intel]

lgtm.

Overriding pullapprove as a doc review is not required (code block changes only):

• https://github.com/kata-containers/community/blob/master/Documentation-Review-Process.md#exempt