testsuite: use relative paths, set PATH to absolute path

This approach works better with autotools, which supports the build
directory being complete outside the source tree.

testcases/lib/SocketActivation.pm

@@ -62,14 +62,6 @@ sub activate_i3 {
             mkdir $ENV{XDG_RUNTIME_DIR};
         }
         $ENV{DISPLAY} = $args{display};
-        $ENV{PATH} = join(':',
-            '../i3-nagbar',
-            '../i3-msg',
-            '../i3-config-wizard',
-            '../i3bar',
-            '..',
-            $ENV{PATH}
-        );
 
         # We are about to exec, but we did not modify $^F to include $socket
         # when creating the socket (because the file descriptor could have a
@@ -96,7 +88,7 @@ sub activate_i3 {
         # the interactive signalhandler to make it crash immediately instead.
         # Also disable logging to SHM since we redirect the logs anyways.
         # Force Xinerama because we use Xdmx for multi-monitor tests.
-        my $i3cmd = abs_path("../i3") . q| --shmlog-size=0 --disable-signalhandler --force-xinerama|;
+        my $i3cmd = q|i3 --shmlog-size=0 --disable-signalhandler --force-xinerama|;
         if (!$args{validate_config}) {
             # We only set logging if i3 is actually started, but not if we only
             # validate the config file. This is to keep logging to a minimum as

testcases/lib/TestWorker.pm

@@ -125,7 +125,7 @@ sub worker_wait {
 
             package main;
             local $@;
-            do "./$file";
+            do $file;
             $test->ok(undef, "$@") if $@;
 
             # XXX hack, we need to trigger the read watcher once more

testcases/lib/i3test.pm.in

@@ -836,7 +836,7 @@ sub launch_with_config {
     if ($config ne '-default') {
         say $fh $config;
     } else {
-        open(my $conf_fh, '<', './i3-test.config')
+        open(my $conf_fh, '<', '@abs_top_srcdir@/testcases/i3-test.config')
             or $tester->BAIL_OUT("could not open default config: $!");
         local $/;
         say $fh scalar <$conf_fh>;