Add timeout to curl in get_esgf_dist_mirror

[alaniwi]

This:

esgf-installer/esg-functions

Lines 1339 to 1343 in 875df80

	if [ $devel -eq 1 ]; then
	resarray[$m]=`curl -s -L --insecure $m/dist/devel/lastpush.md5|tr -s " "|cut -d " " -f1`;
	else
	resarray[$m]=`curl -s -L --insecure $m/dist/lastpush.md5|tr -s " "|cut -d " " -f1`;
	fi

causes esg-node to hang if a site does not respond.

A timeout should be specified, with some appropriate behaviour if it times out.