Fix branch existence checks of hotfix track

[blooper05]

Fixes #248.

I've fixed branch existence checks of hotfix track command with reference to the following release track command.

gitflow-avh/git-flow-release

Lines 936 to 969 in 3e05e2a

	cmd_track() {
	OPTIONS_SPEC="\
	git flow release track [-h] <name>
	Start tracking release <name> that is shared on $ORIGIN
	--
	h,help Show this help
	showcommands! Show git commands while executing them
	"
	# Parse arguments
	parse_args "$@"
	gitflow_require_version_arg
	# Sanity checks
	require_clean_working_tree
	require_local_branch_absent "$BRANCH"
	run_pre_hook "$VERSION" "$ORIGIN" "$BRANCH"
	git_do fetch -q "$ORIGIN" || die "Could not fetch branch '$BRANCH' from remote '$ORIGIN'."
	git_remote_branch_exists "$ORIGIN/$BRANCH"
	# Create tracking branch
	git_do checkout -b "$BRANCH" "$ORIGIN/$BRANCH" || die "Could not create branch '$BRANCH'."
	run_post_hook "$VERSION" "$ORIGIN" "$BRANCH"
	echo
	echo "Summary of actions:"
	echo "- A new remote tracking branch '$BRANCH' was created"
	echo "- You are now on branch '$(git_current_branch)'"
	echo
	}

Please check my changes and merge them if you can. Thanks!

[ChrisJStone]

I'm in the process of updating gitflow. If you could kindly resubmit your pull request against my fork here as it appears this fork is no longer being updated.