tools: support --no-make-first option in "run-nm-test.sh"

Why? Because I often use a command line like

  $ ./tools/run-nm-test.sh -m src/libnm-client-impl/tests/test-nm-client -p /libnm/device-connection-compatibility

or even alias it to a one character command `x`.
Usually I want to do the rebuild, and as `make` is so slow, it
adds noticeable time running the command. Thus, sometimes I want
to modify the command, for which I have to edit the command from the
history, or toggle two separate commands.

Add a `-M` flag that can reverse the effect of an earlier `-m`.

An "enable" flag in general should just also have a "disable" flag.

tools/run-nm-test.sh

@@ -37,6 +37,7 @@ usage() {
     echo "  --no-libtool: when running with valgrind, the script tries automatically to"
     echo "        use libtool as necessary. This disables libtool usage" 
     echo "  --make-first|-m: before running the test, make it (only works with autotools build)"
+    echo "  --no-make-first|-M: disable --make-first option"
     echo "  --valgrind|-v: run under valgrind"
     echo "  --no-valgrind|-V: disable running under valgrind (overrides NMTST_USE_VALGRIND=1)"
     echo "  -d: set NMTST_DEBUG=d"
@@ -165,6 +166,10 @@ else
             NMTST_MAKE_FIRST=1
             shift
             ;;
+        --no-make-first|-M)
+            NMTST_MAKE_FIRST=0
+            shift
+            ;;
         "--valgrind"|-v)
             NMTST_USE_VALGRIND=1
             shift;