deploy_chef should catch install.sh errors

[tobami]

@henning reported in #201 the following problem.

When specifying a wrong Chef version

$ fix node:default deploy_chef:method=omnibus,version=0.10

the omnibus installer will error out and LittleChef will not catch the stacktrace

Deploying Chef 0.10 using the omnibus installer...
Downloading and installing Chef 0.10...

Fatal error: sudo() received nonzero return code 1 while executing!

Requested: bash /tmp/install.sh -v 0.10
Executed: sudo -S -p 'sudo password:' /bin/bash -l -c "bash /tmp/install.sh -v 0.10"

Standard output

Downloading Chef 0.10 for el...
downloading https://www.opscode.com/chef/metadata?v=0.10&prerelease=false&nightlies=false&p=el&pv=6&m=x86_64
to file /tmp/install.sh.2574/metadata.txt
trying wget...
ERROR 404
Unable to retrieve a valid package!
Please file a bug report at http://tickets.opscode.com
Project: Chef
Component: Packages
Label: Omnibus
Version: 0.10

Please detail your operating system type, version and any other relevant details
Metadata URL: https://www.opscode.com/chef/metadata?v=0.10&prerelease=false&nightlies=false&p=el&pv=6&m=x86_64