jail: Add '-s' options to MAKE_CMD by default

Add '-s' option to MAKE_CMD unless '-v' option of 'poudriere' is
specified. This means less messages are displayed while
building/installing/updating jail from source tree.

src/share/poudriere/jail.sh

@@ -421,6 +421,9 @@ setup_build_env() {
 			err 1 "You need fmake installed on the host: devel/fmake"
 		MAKE_CMD=${FMAKE}
 	fi
+	if ! [ ${VERBOSE} -gt 0 ]; then
+		MAKE_CMD="${MAKE_CMD} -s"
+	fi
 
 	: ${CCACHE_BIN:="/usr/local/libexec/ccache"}
 	if [ -n "${CCACHE_DIR}" -a -d ${CCACHE_BIN}/world ]; then