BRP Python Bytecompile: Avoid hardcoding /usr/bin prefix for python

Avoid using the full path and instead rely on PATH being correctly set
up to find the executable.

This fixes byte compilation for python2.7 when doing flatpak module
builds where python2.7 can be in either /usr/bin or /app/bin, depending
on how it's compiled.

brp-python-bytecompile

@@ -121,7 +121,7 @@ export PYTHONHASHSEED=0
 shopt -s nullglob
 for python_libdir in `find "$RPM_BUILD_ROOT" -type d|grep -E "/(usr|app)/lib(64)?/python[0-9]\.[0-9]+$"`;
 do
-	python_binary=/usr/bin/$(basename $python_libdir)
+	python_binary=$(basename $python_libdir)
 	real_libdir=${python_libdir/$RPM_BUILD_ROOT/}
 	echo "Bytecompiling .py files below $python_libdir using $python_binary"