install_prereq: Support package manager DNF and yum option strict=1.

This re-enables the script ./contrib/scripts/install_prereq on Fedora 22 and
newer, and on RHEL/CentOS when the option strict=1 was set for yum install.

ASTERISK-27598
Reported by: Hunter Stevens, Said Masoud

Change-Id: I40f9517122aaa6906e8fc0962b4b8008dfddb368

contrib/scripts/install_prereq

@@ -124,7 +124,7 @@ handle_debian() {
 handle_rh() {
 	extra_packs=`check_installed_rpms $PACKAGES_RH`
 	if [ x"$extra_packs" != "x" ] ; then
-		$testcmd yum install -y $extra_packs
+		$testcmd yum install --skip-broken --assumeyes $extra_packs
 	fi
 }