Does not import automation tools on setup

Not importing automation tools will not raise ImportError due to on
setup time Fabric dependency would not be available.

Fixes #80
Improve setup_abrt task

First check if the rubygem-smart_proxy_abrt is available. If available
proceed with the installation, else print a warning and do anything.

Closes #70
Merge pull request #91 from elyezer/improve-setup

Does not import automation tools on setup
Merge pull request #93 from elyezer/improve-setup-abrt

Improve setup_abrt task
Improve update_system task

Now the task accepts positional arguments which will be passed to yum
update command. If no positional arguments are provided, then will
update all packages.

Also replace all occurrences of yum update with update_system task call.

Closes #90
Merge pull request #92 from elyezer/improve-update-system

Improve update_system task