python-semanage: fix cross-compilation, add test.sh

python-semanage: fix cross-compilation, add test.sh

Add HOST_PYTHON3_PIP_VARS and --no-build-isolation to MAKE_VARS.
Without --no-build-isolation, pip creates an isolated build environment
which fails during cross-compilation because _sysconfigdata is missing.
Aligns with python-selinux which already has this fix.

The libsemanage pywrap uses the host Python's EXT_SUFFIX to name the
C extension, so we will use the PYCEXT env-var to correct that.

Add basic test.sh to verify the semanage Python bindings load correctly
in environments without SELinux kernel support.

Signed-off-by: Alexandru Ardelean <redacted>