Bugfix gdb.debug: exe parameter now respected

[goreil]

This commit now properly supports the exe parameter in pwnlib/gdb.py:debug(), allowing a different argv[0] than the executable. (See Issue #1273 )

It achieves this by leveraging the gdbsever--wrapper argument with a python script that calls execve with the specified args.
For remote connections ssh.process(run=False) already creates a python script that we can use.

Details

1. We create a python script, that calls execve with our arguments
   /tmp/pwn-XXXXXX.py

#!<local python version>
import ctypes
...
ctypes.CDLL(None).execve(exe, argv, env)

2. gdbserver has no native support for argv[0]

Therefore we leverage the --wrapper flag, which allows us to execute an arbitrary command. gdbserver will attach to the first unforked execve system call.

The command will then be
gdbserver --wrapper /tmp/pwn-XXXXXX.py -- <other gdbserver args>

[goreil]

How does a libcdb.rst test fail? I only changed ssh.py and gdb.py and Changelog.md

Document: libcdb
----------------
**********************************************************************
File "libcdb.rst", line ?, in default
Failed example:
    'main_arena' in ELF(filename).symbols
Expected:
    True
Got:
    False
**********************************************************************

[peace-maker]

The libcdb tests are flakey since they rely on external services unfortunately. You can ignore them.

[goreil]

There is an argument to be made to rename exe to executable, since that is the name of the parameter in tubes.process or ssh.process.

But since that might break something I recon we do that in a seperate Pull request.

[goreil]

Closing and opening new pull request, since coveralls seems broken when changing target branch.

[peace-maker]

We don't look at coveralls output right now, so no need to worry about it.