Add error handling

[MarcusSmith]

Add error handling to deal with external commands. (security cms, codesign, etc)

[MarcusSmith]

to get rid of stdout and only print stderr to variable:

err="$(function args 1>/dev/null)"

[MarcusSmith]

Use something similar to this? (from floatsign.sh: https://gist.github.com/Weptun/5406993)

function checkStatus {

if [ $? -ne 0 ];
then
echo "Had an Error, aborting!"
exit 1
fi
}

[MarcusSmith]

Make it easy to handle errors to pass back up to Resign Service