update docker stuff

[firefart]

This PR changes the following:

• Add the rebuild parameter to msfvenom
• Add a msfvenom-dev binstub so the local directory gets mounted
• Fix a bug in the gemspec. Currently we have no git binary in the Dockerfile but when running a *-dev binstub the local directory including the .git dir is added so we hit this if branch and ruby tries to execute git. This change searches the PATH environment variable for a git binary.

Error message before this change (run MSF_BUILD=1 msfconsole-dev):

[!] There was an error parsing `Gemfile`: 
[!] There was an error while loading `metasploit-framework.gemspec`: No such file or directory - git. Bundler cannot continue.

 #  from /usr/src/metasploit-framework/metasploit-framework.gemspec:28
 #  -------------------------------------------
 #    if File.directory?(File.join(File.dirname(__FILE__), ".git"))
 >      spec.files         = `git ls-files`.split($/).reject { |file|
 #        file =~ /^documentation|^external/
 #  -------------------------------------------
. Bundler cannot continue.

 #  from /usr/src/metasploit-framework/Gemfile:4
 #  -------------------------------------------
 #  #   spec.add_runtime_dependency '<name>', [<version requirements>]
 >  gemspec name: 'metasploit-framework'
 #  
 #  -------------------------------------------

[busterb]

Seems like we're missing some Windows corner cases per https://stackoverflow.com/questions/2108727/which-in-ruby-checking-if-program-exists-in-path-from-ruby but I doubt people are building the metasploit gem from a stock Windows environment.

[firefart]

@busterb I pushed some changes can you please take a look again?

[busterb]

Thanks, looks good to me.

[busterb]

nice, thanks for splitting this out.

[busterb]

Release Notes

The usability of Metasploit in Docker containers has been improved.