selftest/rust: correctly form the PATH environment variable

There were two issues here:

- the path to native python was not included, so the test
suite was running with host python, causing failures due to
host python being given native libraries:
https://autobuilder.yoctoproject.org/typhoon/#/builders/148/builds/1711/steps/12/logs/stdio
(rust recipe uses native python throughout)

- tmp/hosttools was listead ahead of native-sysroot/usr/bin

(From OE-Core rev: 72156282059aa5a013a386eb95f89dc38726326e)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit aec96b5aec8d6b4a5ae8a719ca05bb727a6197cb)
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/lib/oeqa/selftest/cases/rust.py

@@ -208,9 +208,8 @@ class RustSelfTestSystemEmulated(OESelftestTestCase, OEPTestResultTestCase):
             tmpdir = get_bb_var("TMPDIR", "rust")
 
             # Set path for target-poky-linux-gcc, RUST_TARGET_PATH and hosttools.
-            cmd = " export PATH=%s/recipe-sysroot-native/usr/bin:$PATH;" % rustlibpath
-            cmd = cmd + " export TARGET_VENDOR=\"-poky\";"
-            cmd = cmd + " export PATH=%s/recipe-sysroot-native/usr/bin/%s:%s/hosttools:$PATH;" % (rustlibpath, tcpath, tmpdir)
+            cmd = "export TARGET_VENDOR=\"-poky\";"
+            cmd = cmd + " export PATH=%s/recipe-sysroot-native/usr/bin/python3-native:%s/recipe-sysroot-native/usr/bin:%s/recipe-sysroot-native/usr/bin/%s:%s/hosttools:$PATH;" % (rustlibpath, rustlibpath, rustlibpath, tcpath, tmpdir)
             cmd = cmd + " export RUST_TARGET_PATH=%s/rust-targets;" % rustlibpath
             # Trigger testing.
             cmd = cmd + " export TEST_DEVICE_ADDR=\"%s:12345\";" % qemu.ip