improve git-lb-push error messages
let git lb-push print a useful error message if a wrong remote name was specified (e.g. typo). This should distinguish invalid/inapplicable path specifications from invalid remotes. This is LBCORE-1396
let git lb-push print a useful error message if a wrong remote name was specified (e.g. typo). This should distinguish invalid/inapplicable path specifications from invalid remotes. This is LBCORE-1396