Handle errors in commands

Some errors were swallowed entirely, some didn't print the error
message.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Restore sorting of ls output

Signed-off-by: Ben Firshman <ben@firshman.co.uk>
Merge pull request #97 from bfirsh/cli-regressions

Fix CLI regressions
Allow optional override of os and arch in build

With this change machine will still cross-compile for all supported OSes
/ archs by default, but allows user to customize args to the build
script.

Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>
Merge pull request #106 from nathanleclaire/modify_osarch

Allow optional override of OS and arch in build (speed up compilation)
Add .git to .dockerignore

Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>
Merge pull request #107 from nathanleclaire/dockerignore

A few additions to .dockerignore
Only download boot2docker.iso one time

Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>
Make more robust based on feedback from @ehazlett

Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>