url-lib: don't use --progress-bar if TERM=dumb (RHBZ#814713)

Basically, s390 is the only place I've ever seen TERM=dumb, and it's too
dumb to handle '\r', so --progress-bar produces waaaaay too much output.

The normal progress meter only prints something once per second, so
that's reasonable on terminals where '\r' doesn't work.

See also: https://bugzilla.redhat.com/show_bug.cgi?id=814713

modules.d/45url-lib/url-lib.sh

@@ -54,7 +54,12 @@ add_url_handler() {
 
 export CURL_HOME="/run/initramfs/url-lib"
 mkdir -p $CURL_HOME
-curl_args="--location --retry 3 --fail --show-error --progress-bar"
+curl_args="--location --retry 3 --fail --show-error"
+
+# technically "dumb" can handle the progress bar, but the only thing I've ever
+# seen using TERM=dumb is s390 CMS, and it's too dumb for --progress-bar
+[ "$TERM" != "dumb" ] && curl_args="$curl_args --progress-bar"
+
 curl_fetch_url() {
     local url="$1" outloc="$2"
     echo "$url" > /proc/self/fd/0