winexe: Fix translation of the winexesvc binaries to C

winexe: Fix translation of the winexesvc binaries to C

Two small Windows binaries that winexe uses to execute commands on a
remote system, winexesvc32.exe and winexesvc64.exe, are compiled then
translated into a C byte array as hex so that they can be embedded into
the winexe binary. Although the winexesvc binaries were built properly,
the Python method that does the translation to C tried to open them in
text mode, which would have worked in Python 2 before the concept of
bytearrays was introduced, but instead raises an exception in Python 3.
The exception was unfortunately suppressed, so the build didn't stop,
and the winexe binary that was produced was effectively useless because
it didn't contain either winexesvc binary as expected. After winexe
successfully authenticated with a Windows host, it showed the error
message below rather than executing the given command on the remote
system.

$ ./bin/winexe -U karl%password1 -d 2 //192.168.56.3 cmd
winexe_svc_install: dcerpc_svcctl_StartServiceW failed: WERR_BAD_EXE_FORMAT
main: winexe_svc_install failed: NT_STATUS_BAD_INITIAL_PC

This commit fixes that problem by opening the winexesvc binaries in
binary mode rather than text mode when the winexe build script reads
them to translate them to C. Furthermore it adds an additional
sanity check that will cause the winexesvc binary generator commands to
fail if the winexesvc binaries cannot be opened or read correctly to
guarantee that the build does not silently "succeed" if something like
this ever happens again.

Signed-off-by: Karl Lenz <xorangekiller@gmail.com>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>