Adjust Python interpreter in shebangs.

The repository used both: /usr/bin/python and /usr/bin/env python.

The commit adjust the interpreter selection to /usr/bin/env python, such
that e.g. virtuelenvs are respected correctly.

This is needed when the system's Python is at version 3 and one wants a
local virtualenv for Python 2 or the tempita package.

Signed-off-by: Daniel J. Hofmann <daniel@trvx.org>
Pin Python interpreter to Python 2.

Signed-off-by: Daniel J. Hofmann <daniel@trvx.org>
trivial: remove redundant newline in fail() calls.
Merge remote-tracking branch 'remotes/daniel-j-h/python_interpreter'

Conflicts:
	libsel4/tools/syscall_stub_gen.py
	manual/tools/gen_env.py
	tools/invocation_header_gen.py
	tools/syscall_header_gen.py
Fix "incompatible with i386:x86-64" build error.
Ensure elf_i386 emulation when building for ia32.